University of Adelaide · 1 Chapter 1: An Introduction to 1,2-Dioxines. 1.1 Historical Aspects of...
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Transcript of University of Adelaide · 1 Chapter 1: An Introduction to 1,2-Dioxines. 1.1 Historical Aspects of...
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Chapter 1: An Introduction to 1,2-Dioxines.
1.1 Historical Aspects of 1,2-Dioxines.
Endocyclic peroxides are of synthetic and mechanistic interest due to the
presence of an easily cleaved O-O bond.1 3,6-Dihydro-1,2-dioxines (1) are a type of
endocyclic peroxide generally formed by the addition of singlet oxygen to conjugated
double bonds, Figure 1.2,3 1,2-Dioxines of this type will be the focus of this thesis as
they are relatively under-utilised in synthetic chemistry. 1,2-Dioxines have been
known for 70+ years, however, the field of 1,2-dioxine chemistry only became
popular during the 1960’s and 70’s when methods for the generation of singlet oxygen
using photosensitisers became known. This allowed the preparation of a host of 1,2-
dioxine containing molecules with many and varied ring-systems and functionalities.3
During this period, the synthetic utility of 1,2-dioxines expanded greatly and 1,2-
dioxines became a powerful tool for the incorporation of 1,4-oxygen functionality into
molecules.
1,2-Dioxines and other classes of cyclic peroxide have been identified as
products from the enzymic and non-enzymic decomposition of polyene lipids.4,5
Recently, natural products that contain cyclic peroxides possessing unique
bioactivities have been discovered, Figure 1. The cyclic peroxides Artemisinin6
(Qinghaosu) (2) and Yingzhaosu A7-11 (3), isolated from the Chinese herbal medicines
Artemisia annua L and Artobotrys ucinatus (L) Mer. show marked activity against the
malaria causing parasite P. falciparum and have been the subject of some 1000+
scientific publications in the last 24 years. Importantly, the cyclic peroxide is key for
the mechanism of action in both instances.
Cyclic peroxides possessing cytotoxic activity such as the terpene
Mycaperoxide H (4) have been isolated from the Thai marine sponge Mycale sp.12
The endoperoxide Plakortide H (5), isolated from the marine sponge Plakortis sp.,13,14
shows potent antifungal activity. The net result of these findings is a renewal of
interest in the synthesis and reactions of cyclic peroxide containing molecules.
2
Figure 1. A 1,2-dioxine and some cyclic peroxide containing natural products.
OO
Me
MeHO
HO
Me
Me
OO
Et
EtEt
OMe
O
Plakortide H
Yingzhaosu A
OO
OOH
Mycaperoxide H
O
O
O
OO
Atemisinin
2
3
4 5
OOR1 R2
1
1.2 The Synthesis of 1,2-Dioxines.
With the increased interest in cyclic peroxides generated by the discovery of
bioactive cyclic peroxides, new methods for their synthesis are constantly being
developed.15,16 Even so, by far the most general and popular method for the synthesis
of 1,2-dioxines (1) is the photosensitised [4π+2π] cycloaddition of singlet state
oxygen (1Δg) to a 1,3-butadiene.2,3 The reaction is designated a Type 2 photooxidation,
a designation that infers the presence of singlet state oxygen as a reactant.17
The mechanism of the [4π+2π] reaction is well understood and can be
summarised as follows. When an oxygen saturated solution of a suitable dye is
irradiated; the photosensitizing dye absorbs a photon and becomes excited. The
photosensitisers most commonly now in use are tetraphenylporphine and rose bengal,
however, more efficient sensitisers have recently been reported by Barrett et al.18,19
The excited state dye then transfers its energy to triplet state oxygen generating singlet
state oxygen. The oxygen can then interact with a 1,3-butadiene through a number of
competing processes. These are the [4π+2π] cycloaddition, [2π+2π] cycloaddition and
ene processes yielding 1,2-dioxines (1), 1,2-dioxetanes (6) and hydroperoxides (7)
respectively. The reaction products for the three competing processes obtained for the
photooxidation of (E,E) 2,4-hexadiene (8) are shown in Scheme 1.20
3
Scheme 1
Sensitizer
Sensitizer*
hvO O
O OMe
MeMe Me
ene
Me
Me
OO
[2+2]
Me
Me
O O
s-trans s-cis
OOMe Me
[4+2]
O
MeMe
OOH
1a
8a 8b
6
7
Several different factors influence the competition between the three
processes. The formation of the 1,2-dioxine relies on the presence of a population of
the s-cissoid conformation of the 1,3-butadiene (8b). Furthermore, the distance
between the 1- and 4-carbons of the butadiene is very important in determining the
rate at which addition of singlet oxygen occurs. Thus, in cyclic systems where there is
conformational restriction keeping the 1- and 4-carbon atoms in close proximity, an
enhanced rate of reaction and a preference for [4π+2π] addition over ene and [2π+2π]
addition is seen.2,21 As a consequence, the majority of papers describing 1,2-dioxines
and their reactions relate to bicyclic dioxines derived from cyclic 1,3-dienes.
1,2-Dioxines may also be synthesised under conditions that do not rely on
singlet oxygen. In a Type I process Lewis acid catalyst “dyes” interacts with the diene
giving rise to an excited state diene which then reacts with oxygen via a radical chain
mechanism giving rise to photo-oxidation products. The “dyes” in these cases are
usually Lewis acid catalysts that initiate the reaction by electron transfer reactions
generating diene radical cations. The reaction relies on the use of polar solvents to
stabilise the solvent separated ion-pairs and does not occur in non-polar solvents.22
4
1.3 Synthetic Utility of 1,2-Dioxines.
The ability to perform functional group manipulation or rearrangements on the
1,2-dioxines is necessary to effectively utilise 1,2-dioxines in synthesis. The
development of reaction conditions for the selective transformation of 1,2-dioxines
has therefore been pursued in the field of peroxide chemistry. A consolidation of most
of the processes that have been developed or investigated for both mono and
polycyclic 1,2-dioxines is given in Scheme 2.
Scheme 2
OO
OO
OHOH
OHOH
OOO
R
ab
c
d
e
OO
OOO
X
X
OHO
O
O
fg
h
O
i
1.3.1 Reduction of 1,2-Dioxines.
Processes a-d in Scheme 2 are all reductions that 1,2-dioxines may undergo
depending on the reaction conditions. Process a is interesting as it is a selective
reduction of the alkene portion of the molecule whilst leaving the sensitive and readily
reduced peroxide linkage intact. The reaction of diimide with 1,2-dioxines usually
yields saturated peroxides from 1,2-dioxines through this process and is the only
reliable method to date for the reduction.23-25 An example is the reduction of bicyclic
endoperoxide (9) which when treated with diimide gave the fully saturated bicyclic
peroxide (10) in 30% yield.26
5
Scheme 3
OO
OO
HN=NH
-78 oC9 10
Process b involves simultaneous reduction of both the peroxide linkage and
the alkene of the 1,2-dioxine and is accomplished using hydrogenation over Pt or Pd
catalysts.27,28 The selective reduction of the peroxide linkage (Process c) is much
easier to accomplish than that of the olefin. Metal hydrides such as LiAlH4 reduce
1,2-dioxines to the 1,4-dihydroxyalkenes in high yield and at low temperature.29
Thiourea/methanol is another exceptionally mild reagent for reducing the peroxide
bond. Balci et al. has used the reaction extensively and it is now the reduction method
of choice when reducing cyclic peroxides.1,30,31 An example where the reaction has
been used in the synthesis of a natural product is the preparation of Stipitatic acid
derivatives (12) from 1,2-dioxine (11), Scheme 4.
Scheme 4
O O RO
OR
O
OOH
OH
O
RHO(NH2)2CS
11 12
The reaction of trivalent phosphorus compounds with 1,2-dioxines also gives
reduction of the 1,2-dioxine ring, Scheme 5, Process d. The reaction proceeds by
initial insertion of the phosphine into the peroxide bond, then P-O bond scission to
give an ionic intermediate.32,33 Depending on the conditions employed and the
functionality of the 1,2-dioxine, several outcomes are possible. In bicyclic 1,2-dioxine
(13) where the double bond has been removed, decomposition of the phosphorus
containing intermediate occurs on workup or from atmospheric moisture to give an
anti-1,4-diol (14).34 In bicyclic systems with a double bond present such as (15),
‘attack’ of the intermediate oxygen nucleophile onto the double bond with elimination
generates allylic epoxides (16).35 Both processes furnish triphenylphosphine oxide or
trialkyl phosphate as a byproduct from the reaction.
6
Scheme 5
OOO
OO
OO
Ph3P
O
O PPh3
H2O
OH
OH1314
15 16
H+
1,2-Dioxines may also undergo acid catalysed rearrangement to 1,2,4-
trioxanes in the presence of ketones and aldehydes, Process e.36,37 The original
discovery of this reaction by Jefford et al. was made when bicyclic dioxine (17)
rearranged to the 1,2,4-trioxane (18), Scheme 6. The discovery was timely as the
antimalarial properties of Artemisinin (2) (a 1,2,4-trioxane) had only recently been
established.38,39 The group has since synthesised a number of antimalarial 1,2,4-
trioxane containing molecules by this method.40,41
Scheme 6
OMe
OMe
OMe
OMe
OMe
MeO
OO
OO
O
R
H+
RCHO
17 18
O2
1.3.2 Addition to the Double Bond of 1,2-Dioxines.
The double bond of 1,2-dioxines is reactive to electrophilic reagents and may
be modified without disrupting the peroxide linkage. The two most common
modifications are either halogenation or epoxidation. Epoxidation is usually carried
out with peracids such as m-CPBA or CF3CO3H, and halogenation with bromine or
chlorine in dichloromethane. Both of these processes were carried out on the 1,2-
dioxine (19) obtained from the lipid methyl ricinoleate to give epoxide (20) and 1,2-
dibromide (21), Scheme 7.4
7
Scheme 7
O OH3C(CH2)5 (CH2)7CO2Me
O OH3C(CH2)5 (CH2)7CO2Me
O
O OH3C(CH2)5 (CH2)7CO2Me
BrBr
Br2m-CPBA 19
20 21
1.3.3 Metal Catalysed Rearrangement of 1,2-Dioxines.
Processes h and i are both processes that may be catalysed by certain
transition metal complexes. Some transition metal complexes of Co(II),42 Fe(II),43
Ru(II),44 Pd(0)45,46 and Os(II)44 undergo reactions with endoperoxides by a one
electron redox mechanism. The reaction sequence for both monocyclic and bicyclic
dioxines with Co(II) is depicted in Scheme 8 and proceeds as follows: single electron
oxidative addition of the metal to the peroxide bond gives a metal oxygen bond and an
oxygen centered radical that may then undergo 1,5-hydrogen atom abstraction
yielding γ-hydroxyenones (22) (Process h) or 1,2-addition yielding bisepoxides (23)
(Process i).
Scheme 8
OOR R1 O O
R1
R
Co(III)Co(II) H OHO
R R1- Co(II)
1
OO
OO
Co(III)H
O
OCo(III) O
O
22
15 23
- Co(II)
The substitution pattern on the starting 1,2-dioxine is the major factor
governing the product composition from metal catalysed ring-openings of 1,2-
dioxines. A consequence of the syn-arrangement of oxygen atoms in bicyclic
endoperoxides is that the intermediate oxygen centered radical is unable to abstract a
proton α to the peroxide bond. Thus, bicyclic endoperoxides containing an
8
unsaturation afford excellent yields of bisepoxides.47,48 Monocyclic 1,2-dioxines can
afford mixtures of bisepoxides and/or γ-hydroxyenones because of the freedom of
rotation that the intermediate radical species has allowing 1,2-addition and 1,5-
abstraction.
The metal-catalysed ring-opening of monocyclic 1,2-dioxines can be
influenced to favor bisepoxide or γ-hydroxyenone by careful selection of the
transition metal catalyst. The complex Ru(II)(PPh3)2Cl2 is an example of a catalyst
that when allowed to react with 1,2-dioxines promotes 1,2-addition over 1,5-
abstraction and so yields bisepoxides.44 In contrast, square planar Co(II) complexes
with tetradentate ligands such as Co(II)(SALEN)2 (24) and Co(II)TPP (25), Figure 2,
afford quantitative yields of γ-hydroxyenones.42
Figure 2
N N
NN
PhCo
Ph
Ph
Ph
24
25
O
N N
OCo
1.3.4 Base Catalysed Decomposition of 1,2-Dioxines.
The cis-γ-hydroxyenones (22) formed from the reaction with transition metals
may also be prepared from 1,2-dioxines by a base catalysed decomposition known as
the Kornblum-DeLaMare rearrangement.49 The reaction is catalytic in nature and is
promoted by weak bases such as triethylamine, hydroxide or stabilised phosphorus
ylide.50 The mechanism involves removal of the most acidic proton α- to the peroxide
bond then cleavage of the peroxide bond in an elimination type reaction to ultimately
generate a ketone and hydroxyl group.51 The reaction is shown below in Scheme 9 for
both a bicyclic (15) and monocyclic 1,2-dioxine (1).
9
Scheme 9
OO
H
OO
Et3N
R H
R1 H
Et3N
O
O
O
OH
- (H+) + (H+)
OO
R
R1 H
- (H+) + (H+)
OHO
R
R1 H
1526
1 22
Interestingly, strong bases such as LDA have been reported to add directly to
the peroxide bond of the 1,2-dioxine and consequently do not give cis-γ-
hydroxyenone products.52
1.4 Reactivity of cis-γγγγ-Hydroxyenones.
Whether cis-γ-hydroxyenones (22) have been generated from 1,2-dioxines (1)
via the metal catalysed method or the base catalysed method, their instability to
neutral, acidic or basic media means that isolation and storage is in the main not
viable. Under acidic or neutral conditions, the cis-γ-hydroxyenones rapidly
decompose to furans (27) quantitatively through loss of water, Scheme 10.42,46,53 The
majority of papers that discuss metal catalysed ring-opening reactions of monocyclic
1,2-dioxines have reported furan products only and the intermediacy of the cis-γ-
hydroxyenone has only been inferred because of this decomposition.46
Scheme 10
OHOR R1 O R1
HO
RO R1
H2O
R
OR R1-(H2O)
22 27
(H)+
The rearrangement of (22) to furan (27) has severely hindered the use of cis-γ-
hydroxyenones in synthesis due to their transient nature but has allowed the synthesis
of furan natural products. An example is the terpenoid furan solanofuran (29)
10
prepared from the 1,3-butadiene solanone (28) by a photooxidation / ring-opening /
dehydration synthetic sequence, Scheme 11.54
Scheme 11
O O OOO O
O21. Al2O3
2. H+
28 29
Generating cis-γ-hydroxyenones under basic conditions also has its
complications. cis-γ-Hydroxyenones are rearranged to 1,4-diketones by neutral amine
bases such as triethylamine.50,55 The exact reaction mechanism is still yet to be
proven, however, one has been proposed and is outlined for dioxine (30) in Scheme
12. Initial Kornblum-DeLaMare rearrangement of the 1,2-dioxine (30) is followed by
deprotonation of the hemiacetal (31) derived from cyclisation of the cis-γ-
hydroxyenone to give a dienol (32) that then tautomerises to give the 1,4-diketone
product (33). Acyclic cis-γ-hydroxyenone substrates appear to be much more
susceptible to this rearrangement than γ-hydroxyenones that are part of extended ring
systems.
Scheme 12
OO
C(O)CH3
O
C(O)CH3
HOC(O)CH3
O
O
H
NEt3H NEt3
C(O)CH3
HO
OH
30 31 32 33
1.4.1 Other Methods for the Generation of cis-γγγγ-Hydroxyenones.
There have been other reports of cis-γ-hydroxyenone synthesis that do not
involve the use of 1,2-dioxines, Scheme 13. These include; the Stille coupling of an
acid chloride with a vinyl tin compound, A;56 the photochemical reaction of 1-phenyl-
2-propyn-1-one in an alcoholic solvent, B;57 and the borohydride reduction of 1,4-
diketones, C.58,59 The latter two examples yielded furans from the dehydration of the
cis-γ-hydroxyenones as the final products from the reaction.
11
Scheme 13
Ph
OEtOH
HOPh
OMe
OPh Me-(H2O)B
C
hv
OOAr Ar
Ph Ph
HOAr
OAr
Ph Ph
OAr Ar
Ph Ph
-(H2O)NaBH4
A SnR Bu
Bu
OHPhC(O)Cl
Pd(PPh3)4
HOPh
O
Ph
OOH
23% 51%
1.5 Previous Work from within the Taylor Group on 1,2-Dioxines.
In 1998 Taylor et al. reported that the reaction of 1,2-dioxines (1) with stabilised
phosphorus ylides (34) afford diastereomerically pure di- and tri-substituted
cyclopropanes, an example of the reaction is given in Scheme 14.50,60 The two competing
reaction byproducts isolated from the reaction manifold were the dehydrated furan (37b)
and the diketone (36b) catalysed by the presence of acid and base respectively. The
reaction did not require anhydrous conditions and gave cyclopropanes in good yields
under mild conditions.
Scheme 14
OOPh
H
H
HO
Ph
BnO2C PhO
PhO
+
PhPh
+ OPPh3Ph3PCO2Bn
1b
34a
35b36b
O PhPh
37b
+
Yield 35b = 97 %
34a
12
The cyclopropyl moiety is found as a basic structural motif in a variety of
bioactive molecules and natural products both in animals, plants and microorganisms. Its
chemistry can also be exploited to perform rearrangements of synthetic consequence
such as C3-C4, C3-C5, and C3-C7 ring enlargements. Thus, due to its importance in
organic chemistry the group was stimulated to fully investigate the scope of the new
reaction.
1.5.1 The Addition of Phosphorus Ylides to γγγγ-Hydroxyenones.
Careful investigation of the reaction progress of (1b) using 1H NMR showed the
presence of transient cis- and trans-γ-hydroxyenones. This suggested that the ylide was
acting as a mild base, inducing a Kornblum-DeLaMare rearrangement (see Scheme 9) of
the 1,2-dioxine and that the cis-γ-hydroxyenone may have been the key intermediate.
When trans-γ-hydroxyenone (38b) (also isolated from the reaction mixture) was allowed
to react with stabilised phosphorus ylide under identical conditions to that used in the ,
cyclopropanation occurred, however, a major discrepancy was found between yield and
time for completion between trans-γ-hydroxyenone and parent 1,2-dioxine as outlined in
Table 1. The reaction of cis-γ-hydroxyenone on the other hand afforded cyclopropane
rapidly and quantitatively.
Scheme 15
OO
Ph3PCO2Bn
+PhPhHO
PhPhO
OH
Ph1b
Ph
O
Ph3PCO2Bn
Ph
H
H
HO
Ph
BnO2C
22b 38b
34a
35b
34a
14
1.5.2 Mechanism for the Cyclopropanation.
The reaction of cis-γ-hydroxyenone and ylide can be seen as a Michael Initiated
Ring Closure (MIRC) where the leaving group (phosphine oxide) is constituted from cis-
γ-hydroxyenone and ylide during the reaction. The mechanism for diphenyl dioxine (1b)
reacting with benzyl ester ylide (34a) is outlined in Scheme 17. Compatible ester ylides
include methyl, benzyl and other non-bulky groups.
Scheme 17
Ph
H
H
HO
Ph
BnO2C
Ph
H
OH
Ph
O
Ph
OPh3P
BnO2CPh3P
BnO2C
O
Ph
O
Ph
Ph3P
BnO2C
O
Ph
PhH
H HPh CO2Bn
Ph3P O
O
H
+
+ Ph3P O
Major Isomer
Minor Isomer
22b
H35b
42b
43
44
A preferred conformation of the cis-γ-hydroxyenone is where the hydroxyl proton
is hydrogen bonded to the ketone. This both increases the rate of Michael addition and
increases the facial selectivity such that only the least hindered face is “attacked” by the
ylide. After 1,4-addition of the ylide to the least hindered face of the cis-γ-hydroxyenone,
intramolecular cyclisation by attachment of the nucleophilic hydroxyl oxygen to the
electrophilic phosphorus pole occurs giving (43) or (44). This process sets up the cis
relationship of the keto-enolate and bulky group attached to the hydroxyl carbon of the γ-
hydroxyenone. The intermediate (43) then collapses with expulsion of
triphenylphosphine oxide and proton sequestration from the reaction manifold to furnish
the observed cyclopropanes. The major cyclopropane diastereomer formed always has
15
the cyclopropyl proton α to the ketone group trans to the other two cyclopropyl protons
as depicted and is a consequence of the geometry and conformation of intermediate
enolate (43). The minor isomer (42), if formed, derives from the less formed enolate
(44).
Examination of the mechanism outlined above shows that cyclopropanation could
be approached by direct synthesis of the trans or cis-γ-hydroxyenone or through isomeric
epoxide formation. This is indeed the case; synthesis of the trans-γ-hydroxyenones (38f)
can be achieved by addition of ketone stabilised phosphorus ylide (45a) to α-hydroxy
aldehyde (46), Scheme 18.63 Treatment of β,γ-epoxyketones with base also leads to
trans-γ-hydroxyenones.64
As indicated previously, yields compared to cis-γ-hydroxyenone are lower and
reaction times longer as the trans- isomer must first be isomerised to the cis-isomer.
Although thermally induced isomerisation is somewhat effective, it has been found that
this is more efficient if carried out photochemically. Irradiation of trans-enone (38f) in
the presence of a triplet sensitiser gave cyclopropane (35f) in high yield and acceptable
reaction time. This route has been used to prepare enantiopure cyclopropanes starting
from enantiopure α-hydroxyaldehydes which may be derived from accessible starting
materials.63
Scheme 18
OHO
OHPh
O
O
PhPh3P
O Ph
O
OBn
ee>99%
ee>99%, 59%
PhO OHhv,
Ph2CO
46
45a
38f
34a
22f
35f
The reactions of cis-γ-hydroxyenones may be extended to nucleophiles other
than ylides. An example is the phosphonate nucleophile (47). When allowed to react
with cis-γ-hydroxyenones this reagent gave rise to cyclopropanes identical with those
16
when starting with ylide, Scheme 19. The phosphonate anion is markedly more
nucleophilic than stabilised phosphorus ylides and so reaction times were reduced to
only several hours from days.65
Scheme 19
OOR1Ph
R1
H
H
HO
Ph
R2
R2 P(OR)2
O
MeLi
R1H
H HR2
Ph
O
R2 = CN, CO2Me1b R1 = Ph1c R1 = H
Yield = 51-91%
35 42
47
The development of this reaction increased the scope of the cyclopropanation
as it allowed for the synthesis of cyclopropanes that contained groups other than ester
such as cyano and amide. Coupled with the asymmetric ring-opening of 1,2-dioxines
by Co(II) catalysts (39-41), the reaction was used to synthesise cyclopropanes in high
yield with good enantio-control.65
1.6 Other Methods for the Synthesis of the Cyclopropane Motif.
The cyclopropyl motif is an important function as it is found in many natural
products and as it may be used as an intermediate in synthesis due to its latent energy
derived from ring strain. Because of its importance, its construction has been an aim of
generations of synthetic chemists. In order to put the synthesis of the cyclopropanes
derived from 1,2-dioxines into context, it is necessary to give an outline of other methods
developed for the synthesis of cyclopropanes. The major classes of reactions developed
for the preparation of cyclopropanes with high selectivity are outlined below.66
1.6.1 Simmons Smith Cyclopropanation.
This protocol involves the addition of carbenoids generated from Zn-Cu couple,
Zn-Ag couple or diethylzinc and diiodomethane to olefins. Diastereoselectivity is usually
under substrate control; thus, the reactions of trans-olefins generate trans-cyclopropanes
and cis-olefins generate cis-cyclopropanes. An example of a diastereoselective Simmons-
Smith cyclopropanation is given in Scheme 20.67,68 The reaction of monocyclic enone
17
(48) containing an acetal protecting group with the Simmons-Smith reagent afforded an
excellent yield and diastereoselectivity of cyclopropane (49) and a small amount of the
diastereomer (50) with enantioselectivity induced by the acetal protecting group.
Scheme 20
Zn(Cu)
CH2I2
19:1
90% , >99%ee
48 49 50
OO
Ph Ph
OO
Ph Ph
OO
Ph Ph
1.6.2 Transition Metal-Carbene Complexes.
Transition metal catalysed transfer of carbene ligands to olefins is a general
approach to the enantioselective preparation of cyclopropanes.66,69-71 Various chiral metal
complexes have been used including complexes of iron, palladium, cobalt, ruthenium
and rhodium to add carbenes across double bonds. Limitations to this method are in the
use, preparation and handling of quantities of potentially explosive diazo-compounds.
Recently, chiral Salen complexes such as (51) have been exploited as outlined in Scheme
21 giving excellent yields and selectivity for (52) in the cyclopropanation of styrene.72
Scheme 21
CO2ButPh
OMeO
N N
O OMe
Ph Ph
CoButO2CCN2
cis:trans 97:3
up to 99% ee
51 52Br
51
1.6.3 Michael Initiated Ring-Closure (MIRC)
The MIRC designation is used for those reaction sequences that contain a tandem
1,4-conjugate nucleophilic addition step followed by a nucleophilic ring closure step.
The leaving group can be placed either on the conjugate acceptor or on the nucleophile in
the reaction. The general format for the reactions is given in Scheme 22.
18
Scheme 22
EWGX
EWG
EWGX
EWG
EWG
EWG
EWG
RX
EWG
RXR
EWG
-X
The addition of sulfur ylides to α,β-unsaturated aldehydes, ketones and esters
followed by intramolecular cyclisation affords cyclopropanes and is an example of an
MIRC reaction where the leaving group and the nucleophile are initially on the same
reactant molecule. The MIRC reaction has been used by Pyne et al. for the synthesis of
cyclopropyl amino acid derivatives, Scheme 23.73
Scheme 23
O
N
O
O Ph
PhS
OEt
O
O
N
O
O Ph
PhCO2Et
Yield = 55%
53 54 55
The reaction of glycine derivative (56) and α,β-unsaturated ester bromide (57) yields
cyclopropane (58) in high yield and is an example of a MIRC reaction where the leaving
group and the electrophilic reaction fragments are on the same initial molecule. The
reaction has been used recently for the synthesis of constrained amino acids.74
Scheme 24
EtO
ONCPh2
Br CO2MeMeO2C
CO2Et
NH2
1. LiBr, NEt3
2. HCl
Yield = 94%
56 57 58
H
19
1.7 Aims and Targets of Research.
The work described within this thesis was aimed at further developing the
chemistry of 1,2-dioxines in several ways. The first aim was to attempt to increase the
scope of the cyclopropanation reaction previously described. If this was possible then
the synthesis of natural products and other molecules of biological interest could be
attempted. Furthermore, the chemistry of the cyclopropanation products remained
unexamined. Since so many reactions have been developed for the skeletal
rearrangements of cyclopropanes, the application of these reactions to the
cyclopropanes obtained from 1,2-dioxines and ylides is an area that requires
examination.
The second aim was to try and generate new chemistry derived from 1,2-
dioxines or cis-γ-hydroxyenones that had not previously been described. Further
elaboration of the chemistry that may be performed on the 1,2-dioxine ring would
facilitate the use of these compounds in the synthesis of interesting and important
molecules. Furthermore, due to the unique and interesting bioactivities that derive
from the endocyclic peroxide bond, the synthesis of novel 1,2-dioxines are of benefit
and new discoveries could be made pertaining to the bioactivity spectrum.
20
Chapter 2: The Synthesis of 1,2-Dioxines.
The stated aims of this project were to increase the scope of the
cyclopropanation reaction and to further investigate the chemistry of the 1,2-dioxine
moiety. To achieve both of these aims the synthesis of a range of 1,2-dioxines was
required. Different segments of work described within this thesis required different
dioxines. Therefore, for ease of presentation, the syntheses of the 1,2-dioxines are
described separately.
2.1 1,2-Dioxine synthesis.
The addition of singlet oxygen to a 1,3-butadiene is the general route to the 1,2-
dioxine ring-system. The 1,3-butadienes 1,4-diphenyl-1,3-butadiene (61b), 2,4-
hexadiene-1-ol (61h) and 1,3-pentadiene (61i) were commercially available and so
did not require synthesis. Standard phosphorus ylide chemistry was used for the
synthesis of all other 1,3-butadienes according to the general procedure in Scheme 25.
Thus, addition of the unstabilised phosphoranes generated from the phosphonium salts
(60a-e) to commercially available unsaturated aldehydes (59a-e) afforded the known
1,3-butadienes (61d-k) in yields ranging from 60-95%.
Scheme 25
OR1R2
R3
R1R2
R3R4
Ph3P
59a R1 = H, R2 = H, R3 = H59b R1 = Ph, R2 = H, R3 = H59c R1 = Ph, R2 = Me, R3 = H59d R1 = Ph, R2 = H, R3 = Me59e R1 = n-C3H7, R2 = H, R3 = H
60a R4 = H60b R4 = Me60c R4 = n-C4H960d R4 = n-C7H1560e R4 = c-C6H11
R4 (60-95%) 61c R1 = Ph, R2 = R3 = R4 = H 61d R1 = Ph, R2 = Me, R3 = R4 = H 61e R1 = Ph, R2 = H, R3 = Me, R4 = H 61f R1 = Ph, R2 = R3 = H, R4 = Me 61g R1 = C7H15, R2 = R3 = R4 = H 61j R1 = c-C6H11, R2 = R3 = R4 = H 61k R1= n-Pr, R2 = R3 = H, R4 = n-Pr
X
KOBut
The 1,3-butadienes were isolated as mixtures of E and Z isomers about the
new double bond formed in the reaction after chromatography. The stereochemistry of
the alkenes did not affect the addition of singlet oxygen. Under oxygenated sensitised
photolytic conditions, isomerisation of the double bonds within 1,3-butadienes can
21
occur.75,76 This means that when subjected to the reaction conditions, (E,E), (E,Z) and
(Z,Z) 1,3-butadienes all give rise to cis and not trans-1,2-dioxines as the major
product.
The reaction of the semi-purified acyclic butadienes (61b-k) with singlet
oxygen in all cases gave the cis-1,2-dioxines, Scheme 26.
Scheme 26
R1R2
R3R4
O2, hυ
Rose Bengal bis(triethylammonium) salt
OOR1 R4
R2 R3
Yield 1b R1 = Ph, R2 = R3 = H, R4 = Ph 71 %1c R1 = Ph, R2 = R3 = R4 = H 40 %1d R1 = Ph, R2 = Me, R3 = R4 = H 18 %1e R1 = Ph, R2 = H, R3 = Me, R4 = H 47 %1f R1 = Ph, R2 = R3 = H, R4 = Me 74 %1g R1 = C7H15, R2 = R3 = R4 = H 30 %1h R1 = CH2OH, R2 = R3 = H, R4 = Me 72 %1i R1 = Me, R2 = R3 = R4 = H 27 %1j R1 = c-C6H11, R2 = R3 = R4 = H 55 %1k R1= n-Pr, R2 = H, R3 = H, R4 = n-Pr 61 %
61b R1 = Ph, R2 = R3 = H, R4 = Ph 61c R1 = Ph, R2 = R3 = R4 = H 61d R1 = Ph, R2 = Me, R3 = R4 = H 61e R1 = Ph, R2 = H, R3 = Me, R4 = H 61f R1 = Ph, R2 = R3 = H, R4 = Me 61g R1 = C7H15, R2 = R3 = R4 = H 61h R1 = CH2OH, R2 = R3 = H, R4 = Me 61i R1 = Me, R2 = R3 = R4 = H 61j R1 = c-C6H11, R2 = R3 = R4 = H 61k R1= n-Pr, R2 = H, R3 = H, R4 = n-Pr
The yields from the addition of singlet oxygen to the butadiene were variable
and depended on the substitution of the butadiene. Alkyl substituted 1,3-butadienes
can undergo competing ene reactions which lower the yield of the 1,2-dioxine. Thus,
the yields obtained from 1,3-butadienes that had alkyl substitution were lower than
with solely aromatic substitution. This was even more evident when alkyl substitution
was located at the 2 and 3-positions. In many cases, the major contaminant after
photolysis was unreacted starting material, which was removed by chromatography
and could be recycled. Due to its low boiling point, methyl substituted 1,2-dioxine
(1i) was more readily purified by distillation at reduced pressure.
The known 1,2-dioxines (1b),50,77 (1c),50,77 (1e)78 (1f),50,77,79 (1h),18,19 (1i),77
were spectroscopically identical to the reported materials. The remaining 1,2-dioxines
showed the expected resonances in their 1H NMR spectra at ≈ δ 6.0 - 6.4 ppm due to
the vinylic protons and at ≈ δ 4.0 – 5.0 ppm due to the protons at the 3- and 6-
positions. All 1,2-dioxines exhibited molecular ions in their mass spectra consistent
with the molecular formula.
1,2-Dioxines (1l) and (1m) were kindly synthesised and donated for use by
another member of the research group, Figure 3.80
22
Figure 3
OO
1l 1m
OO
The 1,2-dioxines were stored at -15°C in dichloromethane solution to prevent
decomposition and were usable for several months before purification was again
required. Microanalysis was not conducted on the 1,2-dioxines due to the propensity
for decomposition.
23
Chapter 3: The Co(II) Catalysed Ring-Opening of Unsymmetrical
1,2-Dioxines.
As stated in Chapter 1, the ring-opening of 1,2-dioxines 1 can be promoted by
transition metal complexes. The reaction can yield 1,4-diols (62), cis-γ-
hydroxyenones (cis-enones) (22) or (64) and bisepoxides (63), Scheme 27. The types
of reaction products obtained are dependant on the structure of the substrate and the
catalyst used to generate them.
Scheme 27
OO
O
O
R1
OHOHR1
OHOR1
OOM
R1
R1
Metal
1
63
62
22
or
OOR1
M
OOH
R1
64
OR1
R1
OO
37
36
R2
R2
R2
R2
R2
R2
R2R2
R2
The ring-opening reactions of 1,2-dioxines (1) with Fe(II),43,81 Ru(II),44
Pd(0)45,46,82 and Co(II)42,47,48,62,83-86, Os(II)44 and Rh(I)87,88 have been previously
studied. Of all the metals, Co(II) is the most selective metal for the generation of cis-
γ-hydroxyenones. Even so, the reactions of Co(II) with monocyclic 1,2-dioxines have
been limited to symmetrical 1,2-dioxines where R1 = R2. When R1 ≠ R2 there are two
cis-enone regioisomers (22) and (64) that can be formed in the reaction. No studies
have examined the reactions of unsymmetrical 1,2-dioxines where R1 ≠ R2 with Co(II)
and looked at the regioselectivity of the reaction. It is not known what effects the
regioselectivity of the reaction and which product, (22) or (64), is preferentially given
from the rearrangement of non-symmetrical 1,2-dioxines. Moreover, only cis-γ-
hydroxyenones generated from symmetrical 1,2-dioxines using Co(II) and those
generated via the base induced Kornblum/DeLaMare decomposition of 1,2-dioxines
24
have been used in synthesis. A synthesis of cis-γ-hydroxyenones not reliant upon
symmetry or acidity (Kornblum / DeLaMare) is therefore a valuable addition to this
field of chemistry.
To examine the relative quantities of (22) and (64) formed in the ring-opening
it is necessary to examine the reaction mixtures before decomposition as the
information on the regioselectivity is destroyed after rearrangement to the final
reaction products (1,4-diketones (36) and furans (37)), Scheme 27. Alternatively, if
the reaction products are somehow derivitised to give stable compounds, then
information on the regioselectivity can be gained.
Few studies have been performed using metals where the product cis-γ-
hydroxyenones have been characterised before decomposition has occurred. cis-γ-
Hydroxyenones are stable enough to be characterised using NMR when generated
using Co(II) catalysis. The characterisation of a single enone and its cis and trans
hemiketals generated from a symmetrical 1,2-dioxine using Co(II) was first carried
out by Foote and O’Shea using 2D NMR.42 The cis-γ-hydroxyenones were found to
exist in equilibrium with the cis and trans hemiketals that form by cyclisation of the
hydroxyl group onto the ketone. The Taylor group have since reported the
characterisation of several cis-γ-hydroxyenones generated from unsymmetrical 1,2-
dioxines under basic conditions and from symmetrical 1,2-dioxines using Co(II)
catalysis.50
The cyclopropanation described in Chapter 1 involving stabilised phosphorus
ylide and cis-γ-hydroxyenone is a reaction that gives stable derivatives from the
unstable cis-γ-hydroxyenones.50,60 It was conceivable that the reaction could be used
to derivatise the products from the ring-opening and thereby serve as another tool for
determining the selectivity of the ring-opening.
The aim of this work was to examine the regioselectivity of the Co(II)
catalysed ring-opening of unsymmetrical 1,2-dioxines both by direct examination of
enone ratios using 1H NMR and by derivatisation by reaction with stabilised
phosphorus ylides. From the ratios of products it was hoped that some comments on
the selectivity could be made and a model for predicting the regioselectivity could be
developed. This would further extend the synthetic utility of 1,2-dioxines and
hopefully generate new classes of compounds for which there are no current amenable
routes.
25
3.1 The Reaction of 1,2-Dioxines with Co(II).
Dioxines (1c-j) were chosen for this study for their ease of synthesis and
because they contain combinations of groups with varying steric and electronic
properties. The synthesis of the 1,2-dioxines was described in the preceding chapter
and the compounds are numbered so that R1 is the more sterically hindered side of the
molecule.77,79 This numbering system was used so that the two products (22) and (64)
were distinguished on the basis of the steric size of the substituents attached at the
positions R1 – R4.
The 1,2-dioxines (1c-h) were allowed to react with square planar Co(II)Salen
complexes (24) and (39) in CDCl3 or THF to furnish cis-enones (eneals) (22) and (64)
and small amounts of bisepoxides (63), Table 2 and Scheme 28. The product cis-
enones were characterised without isolation using COSY, ROESY, HMBC and
HMQC 2D NMR experiments. From these experiments, it was possible to assign the
resonances within the 1H and 13C 1D spectra to either (22) or (64). Both (22) and (64)
existed in equilibrium with their cyclic hemiketal (hemiacetal) anomeric mixtures (65-
68) and so the ratios in Table 2 represent a composite of the acyclic and cyclic
isomers, Scheme 29. The relative ratios of the cyclic and acyclic isomers measured in
CDCl3 are given in Table 3. cis-Enones (22) existed in equilibrium with the cyclic
hemiacetals, however, in all cases, the acyclic enone was the major form present in
solution. For eneals, (64c), (64d), (64e) and (64g), no eneal was detected in solution,
the molecules preferring to exist in the cyclic hemiacetal form.
The bisepoxides (63) exhibited characteristic peaks in the 1H NMR from δ 2.0
– 4.0 ppm and in the 13C NMR at δ 50 - 60 ppm. The bisepoxides were typically a
mixture of isomers, however, only small quantities of the bisepoxides were seen in the
reaction mixtures and so their isolation and their stereochemical assignment were not
attempted.
In the 1H NMR spectrum obtained from the reaction of (1c) the relative ratios
of all products (22c, 64c and 63c) could be quantified, however, it was not possible to
differentiate the two cyclic hemiacetals (67c and 68c) as peaks were overlapping and
so the two are quoted as a mixture.
26
Scheme 28
OOR1 R4
HOOR1 R4
OOHR1 R4
NN
O OCo
R1 R1
R1 R1
R2R2
24 R1 = R2 = H39 R1 = But, R2 = -(CH2)4-
24 or 39R4
O
O
R1
63
1c R1 = Ph, R2 = R3 = R4 = H1d R1 = Ph, R2 = Me, R3 = R4 = H1e R1 = Ph, R2 = H, R3 = Me, R4 = H1f R1 = Ph, R2 = R3 = H, R4 = Me1g R1 = C7H15, R2 = R3 = R4 = H1h R1 = CH2OH, R2 = R3 = H, R4 = Me
R2 R3 R2 R3
R2 R3
R2
R3
22c R1 = Ph, R2 = R3 = R4 = H22d R1 = Ph, R2 = Me, R3 = R4 = H22e R1 = Ph, R2 = H, R3 = Me, R4 = H22f R1 = Ph, R2 = R3 = H, R4 = Me22g R1 = C7H15, R2 = R3 = R4 = H22h R1 = CH2OH, R2 = R3 = H, R4 = Me
64c R1 = Ph, R2 = R3 = R4 = H64d R1 = Ph, R2 = Me, R3 = R4 = H64e R1 = Ph, R2 = H, R3 = Me, R4 = H64f R1 = Ph, R2 = R3 = H, R4 = Me64g R1 = C7H15, R2 = R3 = R4 = H64h R1 = CH2OH, R2 = R3 = H, R4 = Me
Table 2. Product distribution from the rearrangement of (1c-h) with (24) or (39).
entrya 1,2-dioxine Catalyst solvent temp ratio (22 : 64 : 63)b
1 1c 24 CDCl3 RT 24 : 71 : 5 2 1c 24 THF RT 21 : 77 : 2 3 1c 39 CDCl3 RT 32 : 64 : 4 4 1c 39 CH2Cl2 -10 26 : 71 : 3 5 1c 39 THF RT 23 : 74 : 2 6 1c 39 THF -78 24 : 75 : 1 7 1c NEt3 CDCl3 RT 100 : 0 : 0 8 1d 24 CDCl3 RT 0 : >95 : 0 9c 1e 24e CDCl3 RT 15 : 63 : 11 10 1e NEt3 CDCl3 RT 100 : 0 : 0 11 1f 24 CDCl3 RT 30 : 65 : 5 12 1f 39 CDCl3 RT 45 : 49 : 6 13 1f 39 THF RT 52 : 42 : 6 14 1f NEt3 CDCl3 RT 100 : 0 : 0 15 1g 24 CDCl3 RT 17 : 70 : 13 16 1h 24 CDCl3 RT 0 : 82f : 0
a Reactions were performed on 20 mg of 1,2-dioxine in 0.7 ml of solvent with 1.0-2.0
mol % catalyst. b Ratios were determined by 1H NMR and represent a composite of
the cis/trans hemiacetal/enone mixtures. c 11% Decomposition to furan had occurred
at time of measurement. e 24.H2O was used for the rearrangement. f Absolute yield
determined using phenyltrimethylsilane as internal standard.
27
Scheme 29
HOOR1 R4
OOHR1 R4
22
64
R2 R3
R2 R3
O
R2 R3
R4
R1
HO O
R2 R3
R4
HO
R1
O
R2 R3
R4R1 O
R2 R3
OHR1OH
65 66
67 68
R4
Table 3. Ratios of enone/cyclic hemiketals measured in CDCl3 at 25°C.
dioxine 22 : [65 : 66] a 64 : [67 : 68]a
1c 22c 93 : 65c 7b 64c 0 : [67c 49 : 68c 51]
1d - 64d 0 : 67d 48 : 68d 52
1e 22e 86 : 65e 14ba 64e 0 : [67e 50 : 68e 50]
1f 22f 78 : [65f 11 : 66f 11] 64f 12 : [67f 43 : 68f 45]
1g 22g 78 : 65g 22b 64g 0 : [67g 50 : 68g 50]
1h - 64h 12 : 67h 16 : 68h 72 a Square brackets [ ] indicate that no distinction could be made between (67) and
(68) on the basis of 2D NMR experiment. b Only a single hemiketal is formed upon
cyclisation of the enone.
The assignment of the NMR for the product mixture obtained for (1f) is
discussed to illustrate the complexity of the NMR elucidation of the reaction products
(22) and (64), Figure 4. The 1H NMR spectrum exhibited methyl singlets at δ 1.65,
1.72 and 2.28 ppm. These were assigned to the two hemiketals (67f), (68f) and acyclic
enone (64f) respectively. The spectrum also exhibited a methyl doublet at δ 1.40
attributed to the known enone (22f). Both singlets at δ 1.65 and 1.72 ppm (Figure 4)
exhibited through-bond interactions with the hemiketal 13C resonances at δ 109 ppm
in the HMBC spectrum. The methyl singlet at δ 2.28 ppm exhibited a through-bond
interaction with the carbonyl 13C resonance in the HMBC at δ 200 ppm. The benzylic
resonances in (67f) and (68f) appeared as a broadened triplet at δ 5.72 ppm and a
broadened singlet at δ 5.87 ppm due to the unresolved small couplings. The two pairs
of vinylic protons were in the range δ 5.94 - 6.08 ppm and exhibited couplings of 6.0
Hz. This value is in the expected range for that seen in five membered rings.89 Also
28
present were the associated hemiketals (65f) and (66f) in equilibrium with the known
enone (22f) in less than 5% of the total amount of product. These were assigned by
comparison with the authentic spectra.61
It was not possible to assign aryl resonances in the 13C NMR of the
enone/hemiketal mixtures to specific isomers and so aryl 13C resonances were not
assigned. Furthermore, the 2D ROESY NMR obtained for (67f / 68f) did not yield
diagnostic through space interactions that could be used to identify the anomer as
either cis or trans. This was a general trend seen through most of the 2D ROESY
NMR’s of the hemiketals (65-68) which prevented assignment in most instances.
Figure 4. 1H NMR assignments for the product mixture obtained from (1f).
HOOPh Me
OOHPh Me
22f 64f
H H H H
O
H H
MePhO
H H
OHPh OH
68f / 67f
Me
δ 6.43 δ 6.92
δ 1.40
12.0 Hz 12.0 Hz
δ 6.30 δ 6.24
6.0 Hz6.0 Hz
δ 2.28Hδ 4.88 Hδ 5.92
5.4 Hz
δ 5.94δ 6.08
δ 3.85δ 3.50
δ 1.65
δ 2.74
δ 5.72H
1.8 Hz
δ 5.96δ 6.06
δ 1.72
δ 2.79
δ 5.87H
68f / 67f
The reaction of (1d) was the most selective of all the 1,2-dioxines giving
solely (64d). Eneal (64d) existed as a 1:1 mixture of hemiketals. This was one of the
two instances where assignment of stereochemistry at the anomeric carbon was
possible. The two hemiketals could be distinguished by 2D NMR and the relative
stereochemistry of the anomeric carbon assigned on the basis of a through-space
interaction between the ortho protons on the aromatic ring and the hydroxyl proton at
the 2-position, Figure 5. No such through-space crosspeak was observed in the 2D
ROESY spectrum of (67d).
29
Figure 5. ROESY spectrum of (67d) and (68d) showing stereochemistry
O O
HH
HH
Me
O H
OHH
H
Me
H
H
ROESY Interaction
68d
67d
NOE
OH
Decomposition of the ring-opened products obtained from (1e) to furan was a
significant problem. Not only was the decomposition fast, the decomposition of (22e)
was significantly faster than (64e).
The NMR spectra obtained from the Co(II) catalysed ring-opening of dioxine
(1h) showed large methyl singlets at δ 2.27, 1.61 and 1.58 ppm which were attributed
to (64h) and the associated hemiketal (67h / 68h). No significant methyl doublets
could be seen that would indicate the presence of structure (22h). The presence of the
unprotected α-hydroxyl group within 1,2-dioxine (1h) promoted greater selectivity in
the ring-opening than that expected from steric hindrance alone. The mechanism by
which this may occur is discussed later.
It was thought that the steric influences of the substituents within the 1,2-
dioxine on the course of the reaction could be increased if a more substituted ligand
about the Co(II) center was used. Catalyst (39) is a selective catalyst for the hydrolytic
kinetic resolution of terminal epoxides and other asymmetric processes.90,91 The
reaction of (39) with 1,2-dioxines proceeded at a much faster rate than that of (24).
Contrary to what was expected, (39) decreased the steric influence of substituents on
the course of the reaction, compare entries 1 with 3 and 11 with 12. It is known that
30
variations in the substitution of the ligands of Co(II)Salen complexes can have a
dramatic effect on the redox potential of the Co(II) center.92,93 This electronic effect is
not fully understood at this point but catalysis by (39) may involve an earlier
transition state in which the steric requirements of the substituents are less important
in determining the reaction outcome.
A small solvent effect was seen in the ring-opening reaction. The ring-opening
of (1f) was more sensitive to the steric influences of substituents in chlorinated
solvents than in THF, compare entries 12 with 13 Table 2, but no such effect was seen
in the reaction of (1c), compare entries 1 with 2. Temperature had little effect on the
ratios of products obtained from the reaction. Catalyst solubility was an issue and
limited the solvents that could be tested at low temperature.
The reaction of dioxines (1) with Co(II) catalyst (24) in all cases gave cis-
enone (64) as the major product. This corresponded to formation of the Co(III)-O
bond and abstraction of the proton occurring at the least hindered side of the 1,2-
dioxine, Scheme 32. When the rearrangement of (1) is catalysed by base, the
regioselectivity is governed by the acidity of the proton to be removed. This means
that either of the cis-enone isomers (22) or (64) may be obtained by selecting
conditions that make use of either steric or acidity differences in the 1,2-dioxine.
3.2 The Reaction of Ring-opened Products (22) and (64) with Ylide (34a).
Stabilised phosphorus ylides (34) react with cis-γ-hydroxyenones to give
cyclopropanes and with aldehydes to give α,β-unsaturated esters, both in near
quantitative yield. Stabilised phosphorus ylides were therefore an ideal reagent to
derivatise (22) and (64) so that isolable compounds could be obtained and to ensure
that product assignments were accurate. When the mixtures of (22) and (64) obtained
from the ring-opening of (1c,d,f-j) were allowed to react with benzyl ester ylide
(34a), smooth transformation into either the cyclopropanes (35) or (69) or dienoate
(70) was seen, Scheme 30 and Table 4. The reactions of cis-γ-hydroxyenones afforded
cyclopropanes by a 1,4-addition pathway whilst α,β-unsaturated aldehydes afforded
(2E,4Z)-dienoates by a 1,2-addition addition pathway.
31
Scheme 30
OOR1 R4
HOOR1 R4
OOHR1 R4
R2
R2
R1
O
BnO2C
R4
R4
O
BnO2C
R1
OBnO
R1OH
R2
Ph3PCO2Bn
O
O
ROO
22
64
2435c R1 = Ph, R4 = H35f R1 = Ph, R4 = Me35g R1 = C7H15, R4 = H35i R1 = Me, R4 = H35j R1 = c-C6H11, R4 = H
69 R1 = Ph, R4 = Me 70c R1 = Ph, R2 = H70d R1 = Ph, R2 = Me70g R1 = C7H15, R2 = H70i R1 = Me, R2 = H70j R1 = c-C6H11 R2 = H
71 R = H72 R = Ac pyr / Ac2O
1c,d,f-j
34a
34a
34a
Me
O
BnO2C
42i
H
Table 4. Reaction 1,2-dioxines with (34a) catalysed by Co(II)(SALEN)2 (24).
entrya 1,2-dioxine product yield b product yieldb
1 1c 35c 18 (24) 70c 70 (76)
2 1d - - 70d 60
3 1f 35f 33 (39) 69 44 (61)
4c 1g 35g 10 70g 66
5c 1h - - 72 39
6 1i 35i 27d (37) 70i 58 (63)
7 1j 35j 15 (23) 70j 59 (77) a Reactions were performed on 1.0 mmol of 1,2-dioxine with 1.0-2.0 mol% of catalyst
(24) and 1.2 mmol of benzyl (triphenylphosphoranylidene)acetate (34a) in CH2Cl2 (5
ml). b Yield refers to isolated yield, ratios in brackets determined by 1H NMR. c Ratio
could not be determined accurately from the crude 1H NMR spectrum. d Isolated as a
mixture of diastereomers (35i : 42i, 86 : 14).
32
The reactions of eneals (64) that gave rise to dieneoates (70c-j) proceeded
rapidly and usually required less than 48 hours for the consumption of all starting
material. Reactions of alkyl substituted enones such as (35i) and (64f) required up to
two weeks for complete consumption of enone to occur.
Phenyl and methyl substituted cyclopropanes (35c),50,63,94 (35f)50,63,94 (35i)63
and (42i)63 were spectroscopically identical with previously reported material. Other
cyclopropanes were identified using 2D 1H and 13C NMR. The stereochemistry of the
cyclopropanes was identical to cyclopropanes previously reported.50 Vicinal
cyclopropyl protons show a trans-coupling of approximately 4.5 Hz and a cis-
coupling of 9.0 Hz, which allows definitive assignment of stereochemistry to be
made. Methyl ketone cyclopropane (69) showed 3 cyclopropane resonances at δ 2.91
and 2.03 to 2.14 ppm and the expected singlet at δ 2.28 ppm due to the methyl
adjacent to the ketone. The resonance at δ 2.91 ppm showed a 4.8 and 8.1 Hz
coupling and was assigned to the proton α to the phenyl ring on the basis of its
chemical shift. The couplings associated with this proton allowed definitive
assignment of the stereochemistry in (69). The IR spectra of (69) showed two
absorbances due to the 2 carbonyl groups (1737, C(O)OBn; 1698, MeCOC3) and a
molecular ion and microanalysis consistent with the proposed structure. Previous
attempts to synthesise cyclopropane (69) from trans-γ-hydroxyenone have failed.63
The need for interconversion of the trans into cis-γ-hydroxyenone coupled with the
very slow reaction seen for (64f) explain these previous failures.
The dienoates (70c-j) showed the correct number of resonances in the aliphatic
and olefinic region of the 1H and 13C NMR. All dienoates (70c-j) were assigned as
having a 2E,4Z configuration on the basis of a ≈ 15 Hz and ≈ 10 Hz coupling for the
two double bonds. The 15 Hz coupling was seen between the signal at ≈ δ 6.00 ppm
and the resonance at ≈ δ 7.60 ppm which were attributed to the α and β protons. The
resonances at ≈ δ 5.70 and ≈ δ 6.20 exhibited an 11 Hz coupling and were assigned to
the γ- and δ-protons. Not unexpectedly, the signals in the olefinic region of the 1H
spectrum exhibited several long-range couplings (4J or 5J) due to the extended π-
conjugation that exists in the system. The dienoates were typically isolated containing
up to 5% of the 2Z,4Z isomer which could be removed by recrystallisation. The
dienoates (70c-j) underwent slow polymerisation at room temperature and even in
solution if refrigerated over several weeks.
33
The reaction of (64h) with (34a) did not give the ‘expected’ cyclopropane as
the major product but a hydroxymethyl cis γ-lactone (71), which was acetylated to
give (72) for ease of isolation. The formation of lactones from the reaction of cis-γ-
hydroxyenones and ylides has been previously noted and involves the hydrolysis of
intermediate phosphorus containing 1,4-addition products, in this case most likely
promoted by the δ-hydroxyl group, Scheme 31.95 In Table 2, the absolute yield of
(64h) was calculated using an internal standard and found to be 82%. Therefore, the
poor yield of lactone was not attributed to a poor selectivity in the rearrangement of
(1h), but from the non-selective interaction of (64h) with ylide.
Scheme 31
HOOOH
OHOOH
BnO2CPPh3
OOOH
BnO2CPPh3
H2O
64h
O
O
OR
71
Ph3PO +O
72R = H
R = Acpyr, Ac2O
An excellent correlation was seen between the product ratios determined by
NMR experiments and by derivatisation for 3-substituted 1,2-dioxines, see Table 2
and 4. This meant that lengthy NMR experiment with subsequent analysis was not
necessary to examine the regioselectivity of the ring-opening of 3-substituted 1,2-
dioxines as the ratio of cyclopropane:dienoate (cyclopropane) was sufficient. An
important consideration was to ensure that all cis-γ-hydroxyenone had been consumed
in the reaction as alkyl substituted cis-γ-hydroxyenones were slow to react by a 1,4-
addition pathway.
34
3.3 Mechanistic Considerations.
The rearrangement of (1f) with (24) shows that the bond strength of the
abstractable proton is not the primary influence on the course of the reaction, Table 2
entry 6. If it were, then the expected major product from the rearrangement would be
(22f) where abstraction of the benzylic proton had occurred. Instead, abstraction of
the non-benzylic proton occurred to yield (64d). The reaction selectivity must
therefore be governed by other factors.
Unsymmetrical 1,2-dioxines exist in two non-equivalent half-chair
conformations (73) and (76) in equilibrium with a half-boat conformation, Scheme 32.
These conformations may be observed using NMR when CH2Cl2 solutions of 1,2-
dioxine are cooled to -100°C. In the two non-equivalent conformations, one of the R-
groups adopts a pseudo-equatorial position and one a pseudo-axial position due to the
cis nature of substitution on the 1,2-dioxine. The oxygen adjacent to the pseudo-
equatorial position is sterically shielded by the two substituents. Reactions might be
expected to occur at the oxygen on the more accessible face of the 1,2-dioxine. If this
were the case, then factors that affect the equilibrium of the two half-chair conformers
would be expected to influence the selectivity seen in the ring-opening reaction.
Scheme 32
Co(II) OOHR1 R2
- Co(II)
Co(II)OHO
R1 R2
- Co(II)
22
64
O
O
R1 R2
O
OR2R1
O
OR2R1
Co(III)
HH
O
O
R1 R2
H
HH
Co(III)
HH
reactiveoxygen
reactiveoxygen
O OR1 R2
HH
7374
75
76 77
The preference for large groups to exist in pseudo-equatorial positions thereby
relieving steric strain will affect the relative energies of the two half-chair
35
conformations (73) and (76). This will in turn affect the relative populations of the
two conformations and should be visible in the NMR spectra of the 1,2-dioxine when
cooled to low enough temperatures that the two conformations enter slow exchange.
To examine the validity of this model, (1c),(1f) and (1j) were examined by 1H
NMR at low temperature. The conformers of the 1,2-dioxines (1c), (1f), and (1j)
coalesced between –60°C and –70°C and when further cooled to –97°C, slow
equilibration of the two half-chair conformers was observed. The low temperature
NMR of (1c), (R1 = Ph, R2 = H) had diagnostic peaks overlapping and so could not be
used to determine the conformational preference of the molecule. 1,2-Dioxine (1j) (R1
= c-C6H11, R2 = H) showed a clear preference for the large R-group to exist in a
pseudo-equatorial position with a 33:67 ratio of (73) and (76). The proton adjacent to
the cyclohexyl ring was clearly assignable as it lacked the large geminal coupling seen
in the methylene pair at C6, Scheme 32. Assignment of the conformation as
cyclohexyl-equatorial was based upon a downfield shift of the pseudo-axial proton.
In the case of (1f), a 31:69 ratio of the two half chair conformers was
observed, however, the assignment of the two half-chair conformers on the basis of
chemical shift was ambiguous. On the basis of the previous chemical shift argument,
the Ph group appeared to adopt a pseudoaxial position, which seems counter-intuitive
and does not follow the trend set for (1j) or previous examples. The conformational
equilibria of (1j) support the proposed mechanism, however, if conformation were the
sole determining factor in the rearrangement, then a difference in the ratios of (73)
and (76) would be expected for (1f) and (1j) which follows the trends observed in the
ring-opening. There was virtually no difference in the relative quantities of (73) and
(76) for (1f) and (1j), compare 33:67 with 31:69. On the basis of the observed
conformational equilibrium alone, it is unclear whether conformation directs the
selectivity of the ring-opening. It may be that conformational preference is governed
by the same factors that influence the selectivity of the ring-opening, (i.e. the steric
effects of the substituents), but does not itself direct the selectivity of the reaction.
The selectivity observed in the ring-opening reaction of hydroxymethyl
substituted 1,2-dioxine (1h) can be rationalised if the conformation of (1h) is
considered, Scheme 33. The oxygen adjacent to the hydroxyl group is available to
form an intra-molecular hydrogen-bond. In this bonded form, the oxygen (O2) may be
prevented from interacting with the Co(II) complex. Alternatively, the hydrogen bond
may lock the conformation of the 1,2-dioxine into that of (78) or it may polarise the
36
peroxide bond, which in turn directs the selectivity of the rearrangement. The actual
cause for the selectivity is at this point uncertain, but the intimate involvement of the
hydroxyl group in directing this selectivity is clear.
Scheme 33
OOMe
HOOMe
OOHMe
24
1h
HO
HOHO
22h64h
O
O
MeO
H
O
OMe
HO
ReactiveOxygen24
78 791
2
3.4 Intramolecular Michael Addition reactions of the Dienoates (70).
The presence of the hydroxyl group and the α,β-unsaturated ester in close
proximity suggested that the dienoates (70) would be ideal candidates for an
intramolecular Michael addition reaction. Intramolecular Michael addition reactions
have been used extensively for the formation of tetrahydrofurans,96 however, the use
of the reaction for the synthesis of 3,5-dihydrofurans has been ignored due to the
absence of suitable starting materials containing a (4Z)-double bond.
When phenyl substituted dienoate (70c) was allowed to react with a trace
amount of potassium tert-butoxide in THF at 0°C, the solution colour immediately
changed from colourless to brown and TLC showed the absence of starting material
and the presence of two compounds of very similar Rf. Careful purification by flash
chromatography afforded two compounds assigned as (80) and (81), Scheme 34.
Scheme 34
37
PhOH CO2Bn O OPh Ph
CO2Bn CO2Bn
80 81
t-BuOK
THF, OoC
H H
ROESY interaction
5 2
70c48 : 52 (67%)
In the 1H NMR of both these compounds, the signals due to the butadiene at δ
5.00 – 7.60 ppm were replaced by a 1,2-disubstituted double bond at δ 5.91 – 5.99
ppm and an ABX system at δ 2.66 - 2.80 ppm. The two compounds (80) and (81)
exhibited nearly identical 1H NMR spectra, however the benzylic proton (5-position)
in (80) showed a strong ROESY crosspeak with the proton at the 2-position and so
was assigned a cis configuration. The IR spectra of the new compounds showed a
disappearance of the absorbance due to the hydroxyl group at 3400 cm-1 yet still
contained an ester function at 1731 cm-1 which indicated no α,β-unsaturation. The
reaction gave very little selectivity between the two dihydrofurans.
To summarise, the Co(II) mediated ring-opening of 1,2-dioxines is a process
that may be used to generate cis-γ-hydroxyenones regioselectively from
unsymmetrical monocyclic 1,2-dioxines when there is a large steric difference in the
substituents on the dioxine ring. The major γ-hydroxyenone isomers were those with
the γ-hydroxyl function on the more sterically hindered side of the 1,2-dioxine.
Substitutions at both the 3 and 4-positions within the 1,2-dioxine influenced the
selectivity of the rearrangement. The presence of an α-hydroxyl group at the 3-
position within the 1,2-dioxine significantly increased the observed selectivity for the
Co(II) mediated ring-opening of the 1,2-dioxine. The trapping of the cis-γ-
hydroxyenones with ylide is described and it was found that the product ratios reflect
the cis-enone / enal ratios before trapping. The process was used to prepare 6-
hydroxy-(2E,4Z)-dieneoates in moderate yield from mono and disubstituted 1,2-
dioxines. The dienoates thus generated gave rise to substituted 2,5-dihydrofurans
when treated with an appropriate base. The process was also used to generate a cis-γ-
lactone from 4,5-dihydroxy-3-penten-2-one via an addition/hydrolysis sequence.
38
Chapter 4: An Alternative Cyclopropanation Involving 1,2-
Dioxines.
4.1 The Reactions of Bulky Ylides with 1,2-Dioxines.
In the first chapter of this thesis, the cyclopropanation reaction that results
from the reaction of 1,2-dioxines (1) with stabilised phosphorus ylides (34) was
discussed and in the previous chapter this methodology was extended to cis-enones
obtained from unsymmetrical 1,2-dioxines using Co(II) catalysis. Preliminary results
obtained within the group by Avery61,97 had shown that when benzyl and methyl ester
ylides (34a) and (34b) were replaced with bulky t-butyl ylide (34c), additional
cyclopropane isomers were obtained. These two new cyclopropyl isomers were given
the designation of secondary to distinguish them from those primary cyclopropanes
discussed in Chapters 1 and 3, Figure 6. The main difference seen in the two new
isomers was an apparent shift in the position of the cyclopropane ring such that the
products now contained a cyclopropyl ester rather than a cyclopropyl ketone.
Figure 6
R2
R1
O
OBut
O
R2
R1
OOBut
O
R2
OBut
O
R1
O
Primary
R2
OBut
O
R1
O
Secondary
major minor major minor
84 85 82 83
OOR1 R2 +
OPh3P
OBut
1 34c
These new isomers (82) and (83) obtained from the reaction of dioxine and
ylide (34c) were attributed to the bulk of the ester group of the ylide, prohibiting
intramolecular nucleophilic attack of the keto-enolate onto the oxa-phospholane ring
by some sort of steric influence, Scheme 35. At the time that this work was begun,
the mechanism for the reaction was still not determined although the intermediacy of
39
the cis-γ-hydroxyenone in the reaction of 1,2-dioxine and ylide had been established.
The mechanism was independently established by Avery61 and will be discussed later
in this chapter with refinement, however, the use of other ylides for the reaction will
first be presented.
Scheme 35
OOPhPh
Ph
CO2ButPh
O
Ph
CO2ButPh
O
OPPh3
Ph
O
Ph
CO2But
H
?
CO2ButPh3P
1b 84b
82b
34c
The observed isomeric secondary cyclopropanes were attributed to the steric
bulk of the ylide. To test this hypothesis it was considered appropriate to examine
other ylides that contained bulky ester groups. Replacement of the tert-butyl group
with the diphenylmethyl (DPM) group and also the 1-adamantyl group was
considered an appropriate starting point to examine how the sterics of the ester group
affected the reaction. The synthesis of these two new ylides was therefore required.
Scheme 36
HO
OBr
RO
OBr RO
OPPh3
+
1-AdOH
C6H6, p-TosHDean-Stark
1. C6H6, PPh3, Δ
2. 1N NaOH H2O/MeOH
OH
1-Ad =
HO
OBr
Ph2CN2
+ 34d R = DPM 62%34e R = 1-Ad 69%
84a R = DPM84b R = 1-Ad
The synthesis of the two ylides was based upon standard chemistry and is
shown in Scheme 36.98 Diphenyldiazomethane is a common reagent for the synthesis
40
of DPM esters and when allowed to react with bromoacetic acid gave a quantitative
yield of the bromoacetate (84a). Adamantyl bromoacetate (84b) was synthesised by
the acid catalysed esterification of 1-adamantanol and bromoacetic acid in excellent
yield. The two bromoacetates were then converted to the corresponding phosphonium
salts by reaction with triphenylphosphine. Finally, deprotonation with dilute sodium
hydroxide solution afforded the two phosphorus ylides (34d) and (34e) as cream
coloured solids in good overall yield. Slow addition of the base to the ylide salts gave
the best results as this prevented oiling out of the ylides and afforded purer products.
With the bulky ylides in hand, the effect of altering the steric bulk of the ylide
on the reaction of 1,2-dioxine and ylide could be observed, Scheme 37, Table 5.
When the DPM ylide (34d) was allowed to react with (1b) a single cyclopropyl
isomer was formed by 1H NMR and TLC. Isolation and comparison with those
cyclopropanes already in hand showed the product to be solely the primary
cyclopropane (86b). Conducting the same experiment at lowered temperature showed
only trace quantities of the secondary isomer (90b), entry 2. Thus, at ambient
temperature, the steric bulk of the DPM group was not sufficient to give the
secondary cyclopropanes.
In contrast, the reaction of adamantyl ylide (34e) with dioxine (1b) at ambient
temperature led to a mixture of primary and secondary cyclopropanes (87b), (91b)
and (94b). Lowering the temperature again led to an increase and raising the
temperature a decrease in the amount of secondary isomers (91b) and (94b) that were
formed, entries 3-6. Interestingly, the reaction was sensitive to the overall
concentration of reactants. Low concentrations afforded greater yields of the
secondary cyclopropanes (91b) and (94b), compare entries 4 and 7. When the
reactions of dioxine (1b) with ylide (34e) were conducted at -15°C, the reaction
intermediates (discussed later) were stable and it was only upon warming to room
temperature that decomposition to cyclopropane occurred.
From these results it appeared that steric bulk was the determining factor in
directing the reaction towards the secondary isomers although other factors also
contributed to the selectivity. Furthermore, the steric bulk of the ylide (34e) was
sufficient to promote the formation of the secondary isomers.
The reaction was also applied to the mono-substituted 1,2-dioxine (1c), entries
8,9, which when allowed to react with the adamantyl ylide (34e) also gave rise to the
secondary cyclopropanes (91c) and (94c). Again temperature played a role in
41
deciding the selectivity of the reaction. When the reaction of (1c) with (34e) at -15°C
was monitored at low temperature by 1H NMR, no reaction intermediates could be
seen. This indicated that substitution at the γ-position in the cis-γ-hydroxyenone
significantly affects the stability of the intermediate ylides in the reaction manifold
(see later).
Scheme 37
OO
R2
OR3
OR1
O
Primary
R2
OR3
OR1
O
Secondary
R1 R2
R3O
OPPh3
R2
R1
O
OR3
O
R2
R1
OOR3
OPh
OPh
O
1b R1 = R2 = Ph1c R1 = Ph, R2 = H1k R1 = R2 = n-Pr
36a
34a-e
82 R3 = But
91 R3 = 1-Ad90 R3 = DPM92 R3 = Bn
83 R3 = But
94 R3 = 1-Ad93 R3 = DPM95 R3 = Bn
84 R3 = But
87 R3 = 1-Ad86 R3 = DPM35 R3 = Bn
85 R3 = But
89 R3 = 1-Ad88 R3 = DPM42 R3 = Bn
Major
Major Minor
Minor
Table 5. The reactions of ylide (34a-d) with 1,2-dioxines (1b,c,k).
entrya dioxine ylide solvent conc
.
temp
.
ratiob 36a
(%)
1 1b 34d CH2Cl2 0.38 25 86b 97 (67) : 90b 0 : 93b 0 3
2 1b 34d CDCl3 0.38 4 86b 98 : 90b 2 : 93b 0 0
3c 1b 34e CHCl3 0.20 -15 87b 26 (25) : 91b 66 (48) : 94b 8 (6) 0
4 1b 34e CDCl3 0.06 25 87b 30 : 91b 61 : 94b 9 0
5 1b 34e CDCl3 0.06 60 87b 42 : 91b 45 : 94b 6 7
6 1b 34e C6H8 0.06 100 87b 75 (51) : 91b 5 : 94b 0 20
7 1b 34e CDCl3 0.15 25 87b 58 : 91b 35 : 94b 5 2
8 1c 34e CHCl3 0.10 25 87c 19 : 91c 64 (38) : 94c 17 (5) -
9 1c 34e CHCl3 .06 60 87c 79 (60) : 91c 18 : 94c 3 - a Reactions performed with 1.2 equiv. of ylide. b Ratios determined by 1H NMR,
brackets indicates isolated yields of cyclopropane. c Reaction performed at –25 °C for
three days and then allowed to warm to ambient temperature for 3 days before
purification.
42
The cyclopropyl products were characterised using 2D 1H and 13C NMR
spectroscopic techniques. A limited discussion on the spectra of a primary
cyclopropane is given in Chapter 3. The 1H NMR obtained from (87c), (91c) and
(94c) is discussed and fully assigned to illustrate the significant spectroscopic
differences between the primary and secondary cyclopropyl products, Figure 7.
Cyclopropyl protons in (87c) came into resonance at δ 0.98, 1.56, 1.83 and 2.57 ppm.
The proton α to the ketone group at δ 2.57 ppm had couplings of 4.0, 4.8 and 8.0 Hz,
which indicates that the proton has two trans and one cis adjacent cyclopropyl
protons. Thus, it follows that the ketone and ester groups in (87c) are trans to one
another. The methylene adjacent to the ester group appeared as two distinct doublet of
doublets at δ 2.22 and 2.46 ppm. A general feature of the spectra for this series of
cyclopropane was that the proton adjacent to the ketone was much further downfield
than the proton adjacent to the ester in (91c) and the methylene was upfield relative to
that of (91c).
Cyclopropyl protons in (91c) came into resonance at δ 0.76 and 1.24, 1.42 and
1.76 ppm. The proton α to the ester group at δ 1.42 had couplings of 4.3, 4.3 and 8.7
Hz, which indicates that the proton has two cis and one trans adjacent cyclopropyl
protons. Thus, it follows that the ketone and ester groups in (91c) are trans to one
another. The methylene protons in (91c) at δ 3.19 and 2.80 ppm were shifted
downfield relative to those in (87c) due to the greater electron withdrawing nature of
the ketone group. Furthermore, the protons were more widely dispersed which alone
gave an indication as to the identity of the isomer. The methylene protons exhibited a
crosspeak with the ortho protons of the phenyl ring at δ 7.94 ppm in the ROESY
spectrum and were therefore adjacent to the ketone and not the ester. The
cyclopropanes (86) and (87) were always less polar by TLC than (90) and (91) which
aided in the identification of the isomers at a preliminary stage.
The 1H NMR spectra of (94c) appeared significantly different to that of the
other two cyclopropanes. The proton α to the ester at δ 1.66 exhibited couplings of
8.8, 8.1 and 5.2 Hz, which indicated that there were two cis and one trans adjacent
cyclopropyl protons. Thus, it follows that the ketone and ester groups are cis to one
another. The methylene α to the ketone group appeared as an ABX system at δ 3.26 -
3.33 ppm, which was significantly different to the pattern seen in (87c) and (91c).
These methylene protons showed a through-bond interaction with the ketone carbonyl
43
δ 199 ppm in the HMBC spectra of (94c) which indicated that the methylene was α to
the ketone group.
Figure 7. 1H NMR assignments for (87c), (91c) and (94c).
H
OAd
OPh
O H
Ph
O
OAd
O
H H H
H H
H
HH
HH
δ 1.42
δ 0.74δ 2.84δ 3.19
δ 1.75
H
Ph
OOAd
OH H
HHH δ 1.66
δ 1.11δ 0.91
δ 3.33 δ 3.26δ 2.57 δ 2.46 δ 2.22
δ 1.83
δ 0.98δ 1.56 δ 1.23
87c 91c 94c
4.2 The Effect of Alkali Metal Salts on the Reaction of Ylide and 1,2-Dioxine.
As depicted in Scheme 35, the reaction of ylide (34) with cis-γ-hydroxyenone
(22) gave an intermediate enolate that was proposed to undergo a rearrangement that
led to the observed secondary cyclopropanes. As different metal salts can have a
profound impact on the diastereoselectivity of enolates, it was thought that in this case
also, the addition of metal salts may influence the reaction outcome. To determine
whether this was the case or not, the reactions of (34a-e) with (1b,c,k) in the presence
of a selection of salts were examined.
The diastereoselectivity of the reaction of 1,2-dioxine was sensitive to the
presence of added lithium and sodium salts, Table 6 Scheme 37. When no metal salts
were present, the reaction of (1c) and (34a) yielded only (35c). The addition of either
lithium chloride or sodium bromide to the reaction gave up to 19% of the minor
primary cyclopropane (42c), entries 8 and 9. The change in stereoselectivity seen in
the reaction of (1c) and (34a) was attributed to an altered conformation or enolate
geometry in the intermediate enolate (43) or (44), see Scheme 17. Lithium chloride
was also added to reactions of (1b) and (1f) and (34a), however, failed to significantly
alter the ratio of products obtained.
44
Table 6. Reactions of 1,2-Dioxines (1) with Ylides (34a,c-e) in the Presence of Salts.
Additive Ratio (yield)b Entrya dioxine ylide
(mmol)
1 1b 34d 2.0 LiBr 90b (21)
2 1b 34e 0.1 LiBr 91b 52 (45) : 94b 5
3 1c 34e 1.0 LiBr 87c 8 : 91c 83 (58) : 94c 9 (7)
4d 1c 34a - 35c100 (91)
5 1c 34a 0.2 LiBr 35c 84 : 92c 16
6 1c 34a 1.0 LiBr 35c 6 : 92c 83 (40) : 95c 11 (3)
7c 1c 34a 1.0 LiBr 35c 100
8 1c 34a 10.0 LiCl 35c 85 : 42c 15
9 1c 34a 1.0 NaBr 35c 81 : 42c 19 (4)
10e,f 1k 34c 1.0 LiBr 82k 46 (40) : 83k 4
11e, g 1k 34a - 35k (24) : 42k (16) a Reactions were performed on a 1 mmol scale in CH2Cl2 (5 ml) at 25°C with 1.2-1.5
equiv. of ylide. b Ratios determined by 1H NMR, brackets indicates isolated yields of
cyclopropane. c Conducted in 1:1 THF / EtOH. d See reference 50. e Ratio could not be
accurately determined by 1H NMR. Reaction catalysed by the addition of a catalytic
amount of Co(II)(SALEN)2. f Also isolated were small amounts of the alcohols (96)
and (97). g Yield not optimised.
The addition of lithium bromide had the most pronounced effect of all the salts
tested, an effect that was totally different to that seen with lithium chloride. The
addition of lithium bromide significantly reduced the amount of primary isomer in
favour of the secondary isomer, entries 1-3, 5-7, 10. This was an effect seen
irrespective of the size of the ester group on the ylide. Thus, instead of giving primary
isomer (35c), the reaction of dioxine (1c) and benzyl ester ylide (34a) in the presence
of lithium bromide yielded secondary isomers (92c) and (95c) nearly exclusively,
entry 6. Lithium bromide was found to catalyse the reactions and decreased
significantly the time taken for reactions to proceed to completion. Furthermore,
although the solubility of lithium bromide in CH2Cl2 was quite low, the amount of
lithium bromide present in the reaction mixture dramatically affected the reaction
outcome. The reaction of (1c) and (34a) gave greater selectivity for the secondary
cyclopropanes in the presence of 1.0 equiv. rather than 0.2 equiv. of lithium bromide.
45
As no extra lithium cation was dissolved in the solvent (in both reactions the lithium
bromide was present as a suspension) it is possible that the lithium bromide works by
both hetereogeneous and homogenous catalytic processes. Interestingly, the effects of
lithium bromide on the diastereoselectivity were completely negated when the
reaction was conducted in a solvent where the lithium cation was completely solvated,
entry 7.
The diastereoselectivity of the reaction of diphenyl dioxine (1b) was also
susceptible to the effects of added lithium bromide as seen for (1c), entries 1 and 2.
Further to this altered ratio, a significant decrease in the yield of cyclopropanes was
seen in the reactions of (1b) in the presence of lithium bromide, entry 1. This effect
was more pronounced at low temperature and when atmospheric water was not
excluded from the reactions. The use of lithium bromide allowed the preparation and
isolation of DPM ester cyclopropane (90b), which could be compared with the
product seen in the 1H NMR obtained from the reaction of (1b) and (34c) at low
temperature, Table 5 entry 2.
To further study the effect of temperature on the yield of cyclopropane, the
reactions of dipropyl dioxine (1k) and tert-butyl ylide (34c) were examined at low
temperature in the presence of lithium bromide and water, Scheme 38. It was
necessary to catalyse the reactions of (1k) with Co(II)(SALEN)2 as the basicity of the
ylide was not sufficient to catalyse the Kornblum/DeLaMare decomposition of (1k)
due to the absence of sufficiently acidic protons. In addition to the cyclopropanes
(82k) and (83k), there were two polar products (96) and (97) that were isolated from
the reaction of (1k)/(34c)/LiBr (Table 5 entry 10) or (1k)/(34c)/LiBr/H2O (Scheme
38). The yields of (96), (13%) and (97), (35%) were greatest when the solution of
ylide, lithium bromide and dioxine were allowed to stir at –15 °C for 14 days. A small
amount of the major secondary cyclopropane (82k) (14%) was also present in the
reaction mixture. These two compounds (96) and (97) were purified by successive
flash chromatography until they were chromatographically pure. When examined
using 1H NMR, the two products showed extremely complex spectra that appeared as
though the compounds were multi-component mixtures. To examine the possibility
that the compounds were actually in equilibria with other species an attempt was
made to alter the equilibrium and so favour a single compound from which structural
information could be gained. When a small amount of triflouroacetic acid was added
to the solution for NMR, immediate and complete resolution of the spectra took place
46
giving a single new compound from each precursor. These were assigned as lactones
(98) and (99). The identity of the two precursor molecules could then be assigned as
the acyclic hydroxy esters (96) and (97) which appeared as complex mixtures by
NMR due to their equilibria with the cyclic hemiketal anomers (100) and (101). These
hemiketals were visible in the 13C NMR of (96); the spectrum showed signals at δ 95
ppm assigned to C5 in (100).
Scheme 38
Prn
O OO
Prn
O OO
Prn Prn
Prn
O OHPrn
Prn
O
CO2But
OHPrn
CO2But
TFA TFA
Prn
O OPrn
PPh3
CO2But
LiBr
H2O
98 99
O
CO2But
HO
PrnPrn O
CO2But
HO
PrnPrn
96 97
101100
102
2
3
1
4
5
Formation of the acyclic hydroxy esters probably originates from the addition
product (102) by a Lewis acid promoted hydrolysis reaction. The hydrolysis step of
the reaction occurred at both the phosphorus and the carbon centres and therefore both
(96) and (97) were formed in the reaction. The stereochemistry of the carbon centre α-
to the phosphorus was unassignable in (102) as this stereochemistry was lost upon
hydrolysis. This is similar to that described for the hydroxyl containing lactone (71) in
Chapter 3. The relative stereochemistry of the two lactones (98) and (99) was
assigned on the basis of 2D ROESY NMR experiments. The protons adjacent to the
ketone group (assigned on the basis of a through-bond interaction with the ketone in
the HMBC spectrum) showed a through-space crosspeak with the downfield proton
H4 in the ROESY spectrum of the trans-isomer (99), Figure 7. No such crosspeak was
observed in the cis- isomer. Both γ-lactones showed two resonances in their IR spectra
at ≈ 1775 and ≈ 1710 cm-1 attributed to the lactone and ketone carbonyls respectively.
47
Figure 7. Diagnostic ROESY interactions used to assign (98) and (99).
Prn
O OO
Prn
O OO
98
H H H
H HH
H H
992.53 ppm
2.69 ppm
NOE
4.58 ppm
2.99 ppm
4.19 ppm
The formation of hydrolysis products (96) and (97) was favored at low
temperature. This was probably due to an extended lifetime of the phosphorus
containing intermediate (102) at this temperature. From these results a logical
progression was to evaluate the reactions of 1,2-dioxines and phosphorus ylides in the
presence of lithium bromide at elevated temperature to suppress the hydrolysis of the
intermediate. Preliminary investigations were conducted and are introduced in the
following chapter.
4.3 Mechanism for the Secondary Cyclopropanation.
The mechanism for the reaction has been investigated and discussed by
Avery.97 The mechanism proposed in this report will first be introduced before new
mechanistic insights are presented.
When the reaction of diphenyl dioxine (1b) and tert-butyl ester ylide (34c)
was monitored using 1H and 31P NMR at low temperature, two phosphorus containing
intermediates (106) and (107) were observed. These intermediates were found to
decompose to the end-product secondary cyclopropanes with concomitant phosphine
oxide formation when warmed to room temperature and so were identified as being on
the reaction coordinate. Once the structure of the two intermediates had been
determined, a mechanism could be formulated which is outlined Scheme 39.
48
Scheme 39
HOOPh Ph
22b
HOOPh Ph
PPh3
OButO PPh3
OHPh
CO2But
Ph
O1,4-addition
protontransfer
PPh3
OHPh
CO2But
Ph
O
PPh3
OPh
CO2But
Ph
O
PPh3
OHPh
CO2But
Ph
O
PPh3
PhO
CO2But
Ph
HO
PPh3O
Ph
CO2But
Ph
O
H CH2COPh
H
OPPh3
Ph
HO
OBut
H CH2COPh
H
OPPh3
Ph
HO
OBut
103 104
111
105
106107
108
109110
H
H CO2But
Ph H
CH2COPh H
ButO2C H
Ph H
CH2COPh
SN2
Primary Cyclopropanes
83 and 84
8283
1
2
3
4
5
12
3
4
5O
Ph3POBut
Initial 1,4-addition of the ylide to the least hindered face of the cis-γ-
hydroxyenone gives the 1,4-addition product (103). Cyclisation to (104) followed by
proton transfer from the carbon α- to the phosphorus to the keto-enolate generated
from the 1,4-addition gives the oxaphospholane (105). The oxaphospholane was
49
proposed to exist in equilibrium with the ring-opened ylides (106) and (107), although
no spectroscopic evidence for (105) was observed. The ylide (106) and the cyclic
hemiacetal (107) were characterised by 2D 1H and 13C NMR spectroscopy and the
structures confirmed when the crystal structure of the hemiacetal (107) was obtained.
Cleavage of the C-P bond in (105) gives the enolate (108) which collapses via SN2
attack at the C-O-P+Ph3 centre to give the observed cyclopropanes (82b) and (83b).
The ratio of (82b) to (83b) is governed by the energies of the two isomeric
conformations (109) and (110). The equilibrium between the two conformations (109)
and (110) was found to be temperature dependent.97 Low temperatures favored the
collapse of (106) through (109) and therefore increased the amount of major isomer.
The proton transfer from (104) to give (105) was attributed to a
conformational change (112 → 113) in the phospholane caused by the steric bulk of
the ester group prohibiting nucleophilic attack of the ketoenolate onto the
oxaphospholane, Scheme 40. This intimately involves the formation of
oxaphospholane (104) in the reaction mechanism.
Scheme 40
Ph3P OH
R1
Ph
O
ButO2C
HO
HR
H
R
HO
Ph3PButO2C
Ph
O
H
H
Ph3P
Ph
O
CO2But
H
PrimaryCyclopropanes
SecondaryCyclopropanes
104
112
113
The proposed reaction mechanism could also account for the effects of lithium
bromide if the lithium bromide induced a conformational change from (112) → (113)
the same as that caused by the steric effects of the ylide.
The work described in this chapter gives rise to an alternative mechanism if
the effects of steric bulk and lithium bromide on the structures of ylides are
considered. The structure of stabilised phosphorus ester ylide (34) has been
investigated by Snyder99 in a variety of solvents and can be considered as consisting
of the structures (114-117) shown in Figure 8. There exists a partial double bond
50
between the methyne carbon and the carbonyl carbon and therefore restricted rotation
about that bond. At ambient temperature, stabilised phosphorus ylides with non-bulky
esters exist in their cis conformation (116). As the steric bulk of the ylide is increased
or the temperature is decreased, an increase in the amount of trans ylide (115) is seen.
Figure 8. Phosphorus ylide structure.
O
Ph3P OR
OR
Ph3P O
O
Ph3P OR
O
Ph3P OR
115 114 116
117
This dramatic change in the ratio of cis : trans ylide caused by steric bulk and
temperature is mirrored by the change seen in the type of cyclopropane that is formed.
The cis (116) to trans (115) isomerisation can also be promoted by the addition of
trace amounts of lithium bromide.99 This trend is also followed by the primary :
secondary cyclopropane ratio. Lower temperature, increased steric bulk and lithium
bromide all promote the formation of trans ylide (115) and all promote formation of
the secondary cyclopropanes (82) and (83). Furthermore, the effects of lithium are
related to the concentration of available lithium cation, thus, when fully solvated no
change in diastereoselectivity is seen, Table 6, entry 8.100 This result also matches that
seen for the cyclopropanation.
It therefore appears that the primary : secondary cyclopropane ratio is actually
a reflection of the cis : trans ratio of ylide. The question then becomes “what is the
consequence of addition of trans ylide instead of cis ylide to the cis-γ-
hydroxyenone?” To answer this, the intermediate 1,4-addition products (103-5) or
(111) must be examined.
The stereochemistry of the two-stereogenic centres at C3 and C4 in the
intermediate ylide (106) that leads to secondary cyclopropanes match those in the
putative intermediate (111) that leads to the primary cyclopropane, Scheme 39. This
means that cis : trans isomerism in the ylide can not cause a reversal in the facial
51
selectivity of addition to the cis-γ-hydroxyenone and so affect the relative
stereochemistry at the C3 - C4 centres. There is a third stereocentre (C5) in the
addition product (111) and (104) that is formed only transiently in both pathways
leading to primary and secondary cyclopropanes, Scheme 39. This stereocentre is
controlled by whether the ylide adds to the enone in an exo or endo fashion, Figure 9.
Figure 9. Possibilities for the addition of cis or trans ylide to enone (22b).
OO
Ph
Ph
Ph3P
O
OR
O
O
Ph
Ph
Ph3P
ORO
H HO
O
Ph
Ph
Ph3P
ORO
HO
O
Ph
Ph
Ph3P
RO
O
H
The reaction products cannot be used to determine what the relative
stereochemistry of this C5 center is. If the C5 centre is inverted then the C5 proton
may become available such that proton transfer can occur, Scheme 41. Thus,
inversion at the C5 centre giving the oxaphospholane (118) by attack of the trans
ylide may be the “conformational change, Scheme 40” that gives rise to the secondary
cyclopropanes. Inversion at C5 changes the mode of reaction from intramolecular SN2
attack (giving primary isomers) to proton transfer (giving secondary isomers).
Moreover, the previously proposed mechanism requires the formation of
oxaphospholane (104) for the formation of ylide (106), Scheme 40. The
oxaphospholane (104) is not required in this alternate mechanism for the formation of
(106), however, (106) must still give rise to the cyclopropyl products through an
oxaphospholane intermediate (105), Scheme 39 and Scheme 41.
52
Scheme 41
O
Ph3P OR
OR
Ph3P O
115
116
HOOPh Ph
HOOPh Ph
PPh3
OButO
HOOPh Ph
Ph3P OBut
O
1
2 3
4
1 2 3
4
Primary Cyclopropanes
SecondaryCyclopropanes
5
12 3
4
5
Protontransfer
Cyclization and SN2
22b
103
118
HOOPh Ph
Ph3P OBut
O1
2 3
4
5
106
H
H
In conclusion, the reactions of 1,2-dioxines, bulky ylides and lithium bromide
have been investigated. Mechanistic insights into the cause of the altered selectivity
have been gained by studying the effects of addition products on the reaction between
1,2-dioxines and bulky phosphorus ylides. This study has also contributed to
optimising reaction conditions for the selective formation of the secondary
cyclopropyl isomers from the reaction thereby increasing diastereoselectivity. The
cause for the altered selectivity may be inverted relative stereochemistry at the C5
centre in (118) caused by addition of trans ylide. This mechanistic revision does not
affect the previously published mechanism greatly but adds a further level of detail to
that mechanism. This may be used to predict the outcome from other reactions
between stabilised phosphorus ylides and 1,2-dioxines.
53
Chapter 5: C3-C5 Ring-Expansion Reactions of
ββββ-Ketocyclopropyl carboxylates.
In the preceding chapter the synthesis of a range of substituted β-
ketocyclopropyl carboxylates was described. In the course of this work, the reactions
of stabilised phosphorus ylide, 1,2-dioxine and lithium bromide at elevated
temperature were examined. Rather than the expected cyclopropane products, a
previously unobserved product was isolated in low yield, Scheme 42. This
cyclopentene (119b) had a molecular formula identical to the cyclopropyl product.
Furthermore, the compound had three contiguous stereocentres, which was of
synthetic value and mechanistic interest.
Scheme 42
Ph
OH
Ph
O OAd
119b
OOPh Ph Ph3P
CO2Ad
1b 34e
+Toluene / LiBr
110oC / 1 hr
12%
Ph
OPh
O36b 22%
The C3-C5 ring expansion is a known reaction and thus it was thought that the
cyclopentene probably originated from the cyclopropane through a C3-C5 ring
expansion, Scheme 43. It is therefore prudent to first review the C3-C5 ring-expansion
reaction before discussing further C3-C5 ring-expansion reactions of cyclopropanes
derived from 1,2-dioxines.
Scheme 43
Ph
OPh
Ph
OH
PhO
O
Ad
O OAd?
91b 119b
5.1 The C3-C5 ring-expansion reaction.
A review of the literature shows that there are four main types of C3-C5 ring-
expansion reactions, all of which in some way involve vinyl cyclopropanes.101-103
54
They are the thermal;102 metal catalysed;104,105 photochemical106 and the
heterocatalysed107-109 ring expansion reactions. These reactions have been extensively
reviewed and have formed the basis for a large number of natural product syntheses.
A brief overview of each of the reactions is set out below.
The first C3-C5 thermal ring expansion was reported by Neuriter in 1959,
Scheme 44.110 Heating vinyl cyclopropane (120) at 450°C afforded cyclopentene
(122) and a mixture of pentadiene isomers (123). Due to the interesting nature of the
rearrangement the mechanism of the reaction has since been studied both
experimentally and theoretically. The reaction is thought to proceed via a diradical
intermediate (121) that also leads to the observed byproduct pentadienes (123) via a
1,5-H shift.111
Scheme 44
Ea = 49.7 Kcal / mol
120 121 122
reclosure
1,5-H shift
123
The activation energy of the reaction is sensitive to both substitution and to
electronic effects and depending on the substitution pattern about the cyclopropane
ring either the 1,5-H shift product or the cyclopentene may be favored. Electron-
withdrawing substituents promote the radical cleavage step of the reaction and
electron-donating substituents decrease the radical cleavage when substituted at the
bridgehead position. Consequently, dicyclopropane (124) was found to undergo
radical cleavage at the siloxy-substituted end of the molecule affording enol-ether
(127).112 Conversely, the electron donating effect of silicon ensured dicyclopropane
(125) underwent radical cleavage at the unsubstituted end of the molecule affording
(128), Scheme 45.113,114
55
Scheme 45
OSiMe3
SiMe3
OSiMe3
SiMe3
Me3Si
Me3SiO
124
125
127
129
126
128
In a recent study, Reißig et al. proposed the involvement of zwitterionic
intermediates when the vinyl cyclopropane is substituted with both donor and
acceptor groups, Scheme 46.115 The effect of solvent in the thermal rearrangement of
(130) combined with the substantially lower temperatures required to effect the
rearrangement were offered as evidence for the existence of zwitterionic
intermediates.
Scheme 46
MeCO2Me
OMePhCO2Me
Me
MeO
Ph
130 131
+ diastereomers
Decalin, 190 οC, 4 days, 98%DMF, 190 οC, 11 hours, 100%
Δ
The photochemical C3-C5 ring expansion reaction has received considerably
less attention than the thermally induced rearrangement. Both zwitterionic and
diradical species (133) and (134) have been proposed as possible transition states in
photochemical rearrangement of vinylcyclopropane (132), Scheme 47.106
Scheme 47
R
CO2Et
OEt
O
R
CO2Et
R
hv CO2Et
R
132 135
or
133 134
The Pd(0) catalysed reaction of dienyl cyclopropanes containing doubly-
substituted electron withdrawing groups (136) at 25-60 ºC leads to cyclopentenes such
as (138), Scheme 48. This is an example of a metal catalysed C3-C5 ring-expansion
56
reaction. The reaction probably proceeds through a π-pentadienyl palladium /
stabilised anion species (137) obtained by cleavage of the cyclopropane bond.116
Scheme 48
MeO2C CO2MeCO2Me
CO2Me
136 138
Pd (0)
50 οC
87%
CO2Me
CO2Me
Pd
137
The final class of C3-C5 ring expansion that needs to be highlighted contains
those ring expansion reactions involving α-vinylcyclopropyl anions. As opposed to
the high temperatures required to effect the C3-C5 ring expansion in unactivated
systems, α-vinylcyclopropyl anions rearrange at ambient and sub-ambient
temperatures. A related reaction is the base catalysed ring-opening of cyclopropanols
(139) to afford ketones (140) at ambient temperature, Scheme 49.117-119 When R1 in
(140) is vinylic then the anion obtained from the ring-opening can undergo further
reactions such as ring expansion.
Scheme 49
OH
R
R1Base
R
O
R1
139 140
An example of both an oxygen104 (141) and carbon107 (143) centered anion
accelerated ring-expansion is given below in Scheme 50. Together, these examples
demonstrate that cyclopropanes with α-anions on either the cyclopropyl portion or the
vinyl portion of the molecule are strongly activated toward ring enlargement.
57
Scheme 50
OLi
OLi
141 142
CO2Me
O O OHH
H
H
H
22 oC
CO2Et
OTBDSBu4NF, H2O, THF
-10 οC
143 146
CO2Me
O H
H
O
20
CO2Me
O H
H
O
or
144 145
The reaction of (143) with flouride anion gives an enolate that can be
considered as having a negative charge shared between the enolate oxygen and the
carbon α- to the cyclopropane ring. The reaction yields a cyclopentene where the
product has opposite stereochemistry to that expected at the allylic hydroxyl group
assuming a concerted process. The authors suggested that the reaction was possibly
proceeding through a diradical intermediate, however, they did not give a
comprehensive mechanistic analysis to explain the selectivity observed. Both the
homolysis and heterolysis models were offered as plausible mechanisms for the ring-
enlargement of (143). The same conclusions were made by the authors regarding the
rearrangement of (141).
5.2 Reaction of Cyclopropanes (82) and (91) with Base.
How a particular cyclopropane responds to reaction conditions depends on the
substitution of both the vinyl portion and the cyclopropyl portion of the molecule.
Secondary cyclopropanes obtained from the reaction of 1,2-dioxine and a stabilised
ester ylide in the presence of lithium bromide contain an easily enolisable β-ketone
group. Once enolisation occurs, an enolate much like that of the intermediate (144)
shown in Scheme 50 is generated. The investigation on the rearrangements of
cyclopropanes (82) and (91) was therefore focused on enolising the β-ketone group to
possibly induce rearrangement.
Ketones may be enolised in the presence of both Lewis acids and bases. To
generate the more reactive enolate rather than enol, cyclopropanes were allowed to
58
react with a range of bases under different experimental conditions, the results of
which are displayed in Table 7 and Scheme 51.
Scheme 51
R2
CO2R3R1
O
OH
R1R2CO2R3
OH
Ph
Me
CO2But
CO2R3R2
R1
O
CO2AdPh
Ph
O
isomerisation
148
149b R1 = R2 = Ph, R3 = 1-Ad
149f R1 = Ph, R2 = Me, R3 = But
149k R1 = R2 = n-Pr, R3 = But
150
82b R1 = R2 = Ph, R3 = But
82f R1 = Ph, R2 = Me, R3 = But
82k R1 = R2 = n-Pr, R3 = But
91b R1 = R2 = Ph, R3 = 1-Ad
91c R1 = Ph, R2 = H, R3 = 1-Ad
119 R3 = 1-Ad
147 R3 = But
Table 7. The Reactions of β-Keto-cyclopropanes with Base.
entrya starting base Temp yieldsb
material °C 119 / 147 148 149 150
1 91b NaH 25 119b 18 (23) - - 35 (77)
2 91b LiH 25 - - - -
3c 91b LiOH 110 119b 38 - - 8
4 91b LHMDS 25 119b 83 - - -
5d 82f NaH 25 147f - (23) - f - (77) -
6d 82f LHMDS -78 147f - (6) - f - (94) -
7 82f LHMDS 25 147f 78 - - -
8 82b LHMDS 25 147b 80 - - -
9 91c LHMDS 25 119c 85 - - -
10 82k NaH 25 147k -d (10) - k 59 (90) -
11 82k LHMDS 25 147k 84 - - -
12e 82f KHMDS 25 147f 76 (86) 8 (14) - - a Reactions were performed on a 50 mg scale. b Yield refers to isolated product.
Parentheses indicate product ratio determined by 1H NMR. c Reaction time was 3
hours, performed in toluene. d Isolation not attempted. e Reaction performed in a 4:1
ether/toluene mixture.
59
The first base tested with cyclopropanes of type (82) / (91) was sodium
hydride (Table 7, entries 1, 5, and 10). When allowed to react with sodium hydride
(82k) gave two products, a cyclopentene (119k) and an α,β-unsaturated ketone
(149k). Likewise when (91b) was allowed to react with sodium hydride in THF, only
a moderate yield of cyclopentene (119b) was seen, as the major product was the
ketone (150). Styryl compound (150) forms from (149b) through a base catalysed
rearrangement, Scheme 52. When the reaction of (91b) and sodium hydride was
quenched with water immediately after addition of the cyclopropane to the base, a
mixture of what appeared to be (149b) and (119b) resulted. When the crude mixture
of (149b) and (119b) was allowed to react with an additional portion of sodium
hydride, no increase in (119b) was observed. This showed that (149b) was not in
equilibrium with (91b) under basic conditions, that is, intramolecular Michael
addition of the ring-opened ester enolate onto the α,β-unsaturated ketone did not
occur, Scheme 52. Instead, (149b) underwent a double bond migration to give the
styryl isomer (150) by deprotonation at the allylic and benzylic position followed by
reprotonation.
Scheme 52
Ph
O
Ph
AdO
OPh
O
Ph
AdO
OBase
Ph
O
Ph
AdO
OH+
149b
150
BasePh
O
Ph
AdO
O H+
Ph
OPh
AdO
O91b
Changing the base from NaH to LiOH required high temperatures for
consumption of starting material to occur. It was thought that these reaction
conditions (LiOH / toluene / 110°C) would mimic those of the initial reaction from
which the cyclopentenol (119b) was isolated. This reaction generated some
cyclopentenol (119b), (entry 4) but afforded mainly the trans-ring-opened product
(150). It is important to note that the reaction of lithium bromide and cyclopropane
(91b) in toluene at 100°C gave only starting cyclopropane. This indicated that in the
initial reaction conditions, Scheme 42, the ylide probably acted as a base at high
60
temperature and generated a small amount of lithium hydroxide which catalysed the
rearrangement. The reaction was not repeated with the scrupulous exclusion of water.
These initial results obtained for the ring expansion of the β-keto
cyclopropanes were not promising. The isolation of the trans ring-opened products
(149) and (150) indicated a competitive ring-opening of the cyclopropanes to either a
cis (151) or trans (152) open chain intermediate. Of the ring-opened enolates (151)
and (152), only cis (151) could undergo an intramolecular Aldol reaction yielding the
desired cyclopentenol (119), Scheme 53. It was initially thought that the reactivity of
the cyclopropyl ketoenolate (153) formed after deprotonation could be influenced
such that only the cis ring-opened product (151) was formed in the reaction. Changing
cations from sodium to lithium was one way of influencing the reactivity of the
deprotonated cyclopropane (153). The reaction of cyclopropane (91b) with lithium
hydride gave a multi-component reaction mixture from which no cyclopentenol
products were isolated, Table 7, entry 2.
Scheme 53
R2 R1
OR1
O
AdO2CAdO2C R2
R1
O
CO2Ad
R1
O
AdO2CR1
OHCO2Ad
R2
R2
R2
Base
119
91
149
151 152R2 R1
OCO2Ad
H+
or
153
As two cyclopropyl ketoenolates (E and Z) are possible after the initial
deprotonation, it was thought that each ketoenolate could lead to the formation of a
specific ring-opened geometric isomer (151) or (152). It is therefore fortuitous that
there exists means for the selective deprotonation of ketones to afford single
ketoenolate geometric isomers.120,121 Lithium hexamethyldisilazide (LHMDS) gives
exclusively (Z)-ketoenolates at -78°C. The reaction of (82f) with LHMDS at -78°C
gave nearly exclusively trans ring-opening, entry 6. In contrast, the addition of (82f)
to 1.5 equiv. of LHMDS in THF at 25 °C afforded cyclopentenol (147f) in 78% yield,
entry 7. The order of addition was found to be important, if base was slowly added to
the cyclopropane then the yield of cyclopentenol was significantly reduced.
61
Furthermore, best results were obtained when the cyclopropane was added to the base
as a solution in diethyl ether or THF.
This optimised methodology was then applied to a series of cyclopropanes
with various substitution patterns generated in the previous chapter (entries 4, 7-9, and
11-12). All cyclopropanes with bulky ester groups afforded high yields of
cyclopentenols, with most of the products being highly crystalline. The reaction of
(82f) with potassium hexamethyldisilazide (KHMDS) in toluene/ether yielded two
cyclopentenol products (147f) and (148), entry 12. In addition to the ‘expected’
cyclopentenol (147f), a small amount of another isomer (148), easily separable by
flash chromatography was isolated. Initially it was not known what caused the
formation of the new isomer (148), whether it was the different solvent or the
different base. Attempts at increasing the yield of cyclopentenol (148) by performing
the reaction in toluene were unsuccessful as the yield of cyclopentenol (147f)
decreased in favor of the trans ring-opened product (149). The likely genesis of the
minor isomer was attributed to the potassium counterion rather than the mixed solvent
system that was employed for the reaction leading to slightly altered selectivity in the
ring-closure step of the sequence.
5.3 Characterisation of Cyclopentenol and αααα,ββββ-Unsaturated Ester Products.
Stereochemistry for all the products was assigned on the basis of the 2D
ROESY NMR spectra as the use of coupling constants alone was not sufficient for a
reliable assignment due to flexibility within the ring.89 The spectra of both isomers
(147f) and (148) are discussed, the numbering scheme employed for the discussion is
outlined in Figure 10.
Figure 10. ROESY through-space interactions used to assign (147f) and (148).
OHCO2But
Me
HH
HH
OH
CO2But
Me
HH
HH
147f
15
4 3
215
4 3
2
148
H
H
In the ROESY NMR spectra of (147f) a crosspeak was seen between protons
attached to C1 and the methyl group on C5. Another crosspeak was seen between the
62
ortho protons of the phenyl ring at C2 and the proton on C1. The stereochemistry of
(147f) is such that all contiguous groups have a trans relationship. This was
consistently seen in all major products formed in the reactions described in Scheme
50. This was confirmed when the X-ray structure of (119b) was obtained, Figure 11.
Further evidence for the conserved syn relationship between the group attached to C1
and the OH on C2 of the cyclopentene ring came when the X-ray structure of
cyclopentenol (119c) was obtained, Figure 12.
Figure 11. X-ray Structure of Cyclopentenol (119b).
63
Figure 12. X-ray Structure of Cyclopentenol (119c)
.
The 2D ROESY NMR of the minor isomer (148) was used to confirm the
stereochemistry of the three stereocentres. As in (147f) a crosspeak was seen between
the proton attached to C1 and the methyl group on C5 confirming the same relative
stereochemistry about C1 and C5 in the two molecules. A crosspeak was also seen
between the proton on C5 and the phenyl ring on C2 confirming a syn relationship
between the two groups. Compiling this information shows that the minor isomer
isolated from the reaction has opposite relative stereochemistry at the hydroxyl centre
to that of the major isomer.
The rearrangement compound (150) exhibited a 1H triplet at δ 6.30 ppm
coupled with a 2H doublet at δ 3.98 ppm and a singlet at δ 3.48 ppm. The compounds
spectra was significantly simplified due to the absence of chirality in the molecule.
5.4 Mechanism of the C3-C5 Ring Expansion.
In a recent review on the rearrangement shown in Scheme 50, Hudlicky and
Reed did not rule out the possibility that the rearrangement proceeded through a
diradical intermediate.103 If this was the case in the rearrangement of (82) / (91) then
the relative stereochemistry of C1-C5 in the cyclopentene ring should be directly
64
related to the stereochemistry of the starting cyclopropane due to the stereoselective
nature of the radical reaction. If however, the reaction was proceeding through an
open chain zwitterionic intermediate (151) that is freely rotating, then the relative
stereochemistry of the starting cyclopropane should have no influence on the reaction
outcome as all information regarding the relative stereochemistry will be lost in the
intermediate ester-enolate. This could be easily probed as the reaction to generate the
cyclopropanes used in the rearrangement also yielded cyclopropyl diastereomers with
different stereochemistry about the cyclopropane ring. Cyclopropane (83b) has
inverted stereochemistry at C1 compared to (82b). The reaction of (83b) with
LHMDS under the optimised conditions afforded (147b) in good yield, Scheme 54.
This product is the same as that obtained when starting from (82b). This established
that the relative stereochemistry of the cyclopropane at C1 does not affect the relative
stereochemistry of the product and that the reaction is not concerted but has freely
rotating intermediates.
Scheme 54
Ph
Ph
OButO
O
Ph Ph
O OBut
OH
LHMDS
83b 147b (69%)
1
2
3
A mechanistic rationale for the ring-opening and closing of the cyclopropyl
esters can now be presented, Scheme 55. Deprotonation of the cyclopropane α to the
ketone gives either the Z (154) or E (155) ketoenolate. The E isomer (155) cannot
adopt the conformation required for ring-opening to give the cis-olefin due to steric
interactions between the R1 group (for large R groups such as Ph, n-Pr) and the
cyclopropane ring. The Z-ketoenolate is able to adopt both conformations (154a) and
(154b). Conformation (154a) would give rise to an E double bond and therefore could
not yield the ring-expanded cyclopentenol. Conformation (154b) would give rise to a
Z double bond after ring-opening which could further react to afford the final product
(119). After ring-opening, two of the three original stereocentres have been destroyed
in the freely rotating intermediate (151). Thus, both (82b) and (83b) yielded identical
products. The ester enolate (151) then undergoes an intramolecular Aldol type
addition. Models have been developed by Heathcock et al. for the intramolecular
addition of enolates to aldehydes and ketones.121 This makes it possible to predict the
65
identity of the enolate formed after ring-opening occurs. Based upon the product
stereochemistry and assuming a chair-like transition state (156), models indicate an
intermediate Z-ester enolate.120,122,123
Scheme 55
H
H
HR2H
H
HR2
OR1
R1
O
R1
O
O
R1
H
H
HR2
R1
O
R2 R2R2H H H
H R2
HR2 R1
O
H H
R1OH
OR1
LiOO
R1
H
OAd
R2
H
H
H
OOAd
OOAdO
OAd
O
OAd
O
OAd
O
OAd
OAdO
AdO
O
Base +
R1
O
H R2
AdO
O
H+
H+ CO2Ad
R1R2
OH
91
151
152
154
154a154b155
155
156119
149
C3-C5 ring expansions not involving a concerted mechanism have previously
been reported.115,116 A closely related example is the ring-expansion reported by
Larsen et al., who reported that thiocyclopentenes could be prepared from 3,6-
dihydro-2H-thiopyrans.108,109 In this report a cyclopropyl byproduct was isolated from
several analogues and this cyclopropane also led to the observed thiocyclopentene
66
product. It was not determined whether the cyclopropane was an intermediate on the
reaction coordinate or was present in equilibrium with the open chain malonyl anion.
Moreover, the reaction reported herein is not dissimilar to the conversion of
cyclopropanols to ketones, Scheme 49, the only addition being the aldol ring-closure
step of the sequence.
The primary cyclopropane (84b) was also treated with LHMDS, Scheme 56,
however, none of the cyclopropanes tested gave any cis olefinic cyclic or acyclic
products. The generation and reactivity of the ester enolate is significantly different to
that of the ketoenolate. When an ester is deprotonated with LHMDS in THF at
ambient temperature, the E ester-enolate is formed exclusively.121 This result is
opposite to that seen with keto-enolates. It was considered possible that the geometry
of the product double bonds could again be intimately linked to enolate geometry after
deprotonation and it was possible that the Z ester-enolate was the key for generating
cis olefinic products. The procedure for generating Z-ester enolates in 23%
HMPA/THF described by Ireland124,125 failed to afford cis olefinic products at –78°C
and at room temperatures. The reaction of (84b) with LHMDS afforded (157) in
quantitative yield. Eneester (157) showed characteristic α,β-unsaturated ester proton
resonances in the 1H NMR at δ 5.78 and 6.87 ppm. The spectral data for (157) was in
accord with that reported for similar compounds obtained from the thermal
decomposition of the primary cyclopropane.50
Scheme 56
Me
OBut
OPh
O
LHMDS
84b
PhOBut
O Me
O
157 quant.
THF or THF / HMPA
5.5 Rearrangements/Further Reactions of Cyclopentenols.
In an attempt to develop uses for the cyclopentenols thus generated, the acid
catalysed rearrangement of the cyclopentenol to a cyclopentadiene was attempted. It
was thought that by treating the cyclopentenols with a strong acid such as
triflouroacetic acid (TFA) the compounds would undergo elimination of the tertiary
hydroxyl group yielding substituted cyclopentadienes, useful synthons in bi- and
tricyclic ring synthesis. When the reaction of (147b) with 1 equiv. of TFA in CDCl3
67
was monitored using 1H NMR, a mixture of compounds was seen to be formed. When
this mixture was concentrated in vacuo and purification was attempted by flash
chromatography, the mixture of products resolved into a single crystalline product
(158b) isolated in 88% yield, Scheme 57. When the 1H NMR of the purified product
was compared to the mixture before chromatography, its presence could be seen in the
mixture. The product showed the same number of resonances in its 1H and 13C NMR
spectra as the starting material and was assigned as structure (158b) consistent with
(147b) having undergone an allylic migration of the hydroxyl group. Cyclopentene
(147f) when allowed to react with TFA in CDCl3 at ambient temperature also
underwent the same allylic migration to furnish the allylic cyclopentenol (158f) in
69% yield.
Scheme 57
R Ph
OH
ButO O
R Ph
ButO O
HO
1. TFA
147b R = Ph147f R = Me
158b R = Ph 88%158f R = Me 69%
2. SiO2
1
5 4
3
26
It was possible to obtain crystals of the rearranged product (158b) that were
suitable for single crystal x-ray analysis, Figure 13. This allowed unambiguous
stereochemical assignment about the cyclopentene ring and gave information on the
structure of (158b) that was not easily deduced through NMR experiment due to the
non-first order nature of the spectra. As seen in the ORTEP representation of (158b),
the cyclopentene ring is significantly distorted by the intramolecular hydrogen bond
between the OH and the ester moiety. This distortion of the ring causes the protons on
C5 and C6 to show little coupling due to an approximate 90° dihedral angle as seen in
the COSY spectra. This lack of coupling suggests that the solution structure is the
same as that seen in the crystal structure. A long-range 4J coupling was seen between
C4 and C2 and the OH group was shifted slightly downfield at δ 3.49 ppm.
The NMR spectra of (158f) showed a chemical shift and coupling pattern the
same as that seen in (158b). The proton on C6 appeared as a broadened quartet at δ
2.39 ppm. The small magnitude couplings seen in the proton on C6 to C5 and C2 was
the basis for the assignment of (158f).
68
Figure 13. Molecular structure of (158b).
The rearrangement of cyclopentenol (147b) was also investigated using acetic
acid. The reaction did not proceed at all in the presence of 1 equivalent or neat acetic
acid even with warming to 50 °C.
A tentative mechanistic rationale for the rearrangement is presented in Scheme
58. The strong acid (TFA) caused elimination of water to give a phenyl substituted
allyl cation (159). Addition of triflouroacetate anion to the cation from the least
hindered face of the molecule gave an allyl triflouroacetate ester (160). Addition of
silica to the reaction mixture hydrolysed the TFA ester giving the observed products
(158) with net hydroxyl migration. The driving force for the reaction was formation of
the more substituted double bond and possibly the strong intramolecular hydrogen
bond in (158b), seen in both the NMR and crystal structure. The isolation of the
rearranged products was surprising as removal of the proton α- to the ester group
would have yielded a fully conjugated system. This does not occur presumably due to
the strong steric interactions that result from the phenyl ring and bulky ester being
forced into coplanarity.
69
Scheme 58
R Ph
OH
ButO OH+
-(H2O)R Ph
ButO O
R Ph
ButO O
TFAO
OCF3
O
R Ph
ButO O
HO
SiO2
H2O
147b 158
159
160
There is literature precedence for rearrangements of this type. The
rearrangement of bridgehead alcohols on five membered rings giving
thermodynamically stable molecules has been reported previously. An example is that
reported by Smith et al. who found (161) underwent an acid catalysed rearrangement
to give (162), Scheme 59.126 The authors then used the product in their synthesis of
the diterpene (+)-Jatropholones A and B.
Scheme 59
HO SS
OH
O
1% H2SO4
161162
O
H
MeH
H
(+)-Jatropholone A
The cyclopentenols such as (147b) contained a very hindered face and
therefore were thought to be ideal candidates for reactions that involved electrophilic
attack at the alkene as only a single stereoisomer would be formed. Epoxidation was
chosen as a simple test for this theory and so the cyclopentene (147b) was allowed to
react with m-CPBA in dichloromethane at ambient temperature. Rather than a single
epoxidic product, only low selectivity was seen in the reaction and two epoxides (163)
and (164) were isolated in nearly equal yield, Scheme 60. The epoxides were
separable after careful chromatography and crystallisation.
70
Scheme 60
Ph Ph
OH
ButO O
147b
m-CPBA, RTPh Ph
OH
ButO O
Ph Ph
OH
ButO O
O O
56 : 44163 164
87%
The minor isomer was crystallised and its structure determined by single
crystal x-ray diffraction, Figure 14. The minor isomer corresponded to attack from the
most sterically hindered side of the cyclopentene (147b). A full analysis of the
selectivity was beyond the scope of this work, however, should be undertaken if a
synthetic use is found for the epoxides (163) and (164) or derivatives thereof.
Figure 14. Molecular structure of (164).
5.6 Conclusions and Future Work.
The base catalysed rearrangement of (β-ketocyclopropyl)carboxylates is an
interesting rearrangement as it involves a C3-C5 ring enlargement that does not
involve a concerted process. The process allowed the construction of a new class of
cyclopentene products with three contiguous stereocentres in excellent yield and
71
diastereoselectivity. A requisite for high yield was the use of hindered bases at
ambient temperature to ensure formation of Z-ketoenolate. The mechanistic argument
portrayed in this body of work may explain C3-C5 ring enlargements seen in other
systems.
The product cyclopentenes underwent an allylic hydroxyl group migration
when allowed to react with TFA at ambient temperature rather than dehydration. The
products could also be epoxidised, however, selective conditions for the epoxidation
were not developed.
72
Chapter 6: Tetrahydrofuran Synthesis Utilising 1,2-Dioxines.
6.1 Methods for the Construction of the Tetrahydrofuran Ring.
The tetrahydrofuran (THF) ring is common in both natural products and
synthetic bioactive molecules127-129 and so numerous methods for its synthesis have
been developed.130-135 The most commonly reported are: the exo-1,5-addition of oxy-
radicals to carbon-carbon double bonds (A); the intramolecular SN2 displacement of a
leaving group by an oxygen nucleophile (B); the intramolecular 1,4-addition of
oxygen nucleophiles to conjugate acceptors (C), Scheme 61.
Scheme 61
O YO
O Y
O
Y = OR, NR2, Aryl, Alkyl
O R OR
OX
O
A
B
C
X = Cl, Br, OTs
The 1,4-addition of oxygen nucleophiles is normally intramolecular and
proceeds under base catalysis. Compatible conjugate acceptors include α,β-
unsaturated esters,136-139 ketones140,141 and sulfonates.96,142,143 Recently, a special
extension of the 1,4-addition of oxygen nucleophiles was developed by Paquette et al.
and couples the Oxy-Michael addition with an MIRC reaction.144 Thus, the reaction
sequence in Scheme 62 yielding (167) from acceptor (165) and nucleophile (166) is a
formal Oxy-Michael / Michael or OMIMIRC tandem reaction. The authors used the
reaction for the stereospecific construction of a bis-fused THF ring. The compound
(167) was further elaborated into the natural product (+)-Asteriscanolide using a
combination of RCM and ‘ene’ chemistry.
73
Scheme 62
CO2Me
HO
O SO
Tol
O
O CO2MeSO Tol
H O O
HO
H
H
H
165 166 167168
(+)-Astericanolide
The nitrogen version of the reaction, the Aza-Michael / Michael reaction has
been used by Benetti et al. for the construction of (+)-α-Kainic Acid.145 A simple
example from this report is given below to demonstrate the selectivity achieved and
the functional group arrangement that results from the reaction, Scheme 63. The
reaction of methyl vinyl ketone and enester (169) yielded the pyrrolidine ring-
structure (170) as the sole product after 15 days at room temperature.
Scheme 63
Bn
HN CO2Et
O
+
N
O
TBDMSO
OTBDMS
CO2Et
Bn169
170
Both of these examples (Scheme 62 and 63) demonstrate that the hetero-
Michael / Michael reaction sequence is a powerful tool for the sequential formation of
two bonds with good control of the induced stereocentres. The nucleophilic addition
reactions of cis-enones so far described in this thesis all involve the 1,4-addition of
carbon nucleophiles. Numerous examples of the 1,4-addition of oxygen nucleophiles
to conjugate acceptors are present in the literature. Thus, a logical progression of
investigating the chemistry of cis-γ-hydroxyenones was to explore oxygen and other
hetero-nucleophiles.
74
6.2 Tetrahydrofuran Synthesis from 1,2-Dioxines.
When 1,2-dioxine (1b) was allowed to react with the simplest of all oxygen
nucleophiles, OH-, the expected result was the base catalysed Kornblum / DeLaMare
rearrangement of the 1,2-dioxine to the cis-γ-hydroxyenone (22b) then rearrangement
through to 1,4-diketone (36b).50,55 This follows from the assumption that the cis-γ-
hydroxyenone to 1,4-diketone rearrangement occurs with bases other than the amine
type such as triethylamine. However, instead of the expected 1,4-diketone, 3 different
polar dimeric products were isolated, Scheme 64.
Scheme 64
OOPhPh Ph
Ph
O
OLiOH
1b
OHOPhPh
22b
O
O
Ph
O
Ph
PhHO
Ph
3 isomeric structures
36b
The major and most polar product (171b) was assigned as having the structure
shown in Scheme 65. The stereochemistry of the benzylic alcohol stereocentre could
not be unambiguously assigned on the basis of NMR experiment alone and so was at
first left unassigned. A literature search revealed that THF (171b) had previously been
isolated from the aluminum triisopropoxide reduction of trans-1,2-
dibenzoylethylene.146 In this case only a single THF isomer had been isolated along
with other products and no further studies on the reaction mechanism had been
reported. However, the authors did correctly rationalise the reaction outcome as
proceeding through a γ-hydroxyenone intermediate. The reported stereochemistry of
the reaction product was also in agreement with that deduced from the 2D NMR
spectra, however, the relative stereochemistry of the α-stereocentre was not
determined in this report. Conversion of (171b) to the corresponding acetate (172)
using acetyl chloride and triethylamine in THF confirmed the structure of (171b) as
75
being the same as that found in the reduction of trans-1,2-dibenzoylethylene by
comparison of the reported spectral data and melting point.
Scheme 65
O
OPh
Ph
O
Ph
HO
Ph
171b
AcCl / pyr
CH2Cl2 O
OPh
Ph
O
Ph
AcO
Ph
172b
Considering the large number of possible racemic products (24), the reaction
of 1,2-dioxine (1b) afforded products with an acceptable degree of stereocontrol (dr =
50 : 29 : 11). Furthermore, the high yield (90%) of products obtained from the
reaction made the dimerisation of cis-γ-hydroxyenones of possible synthetic utility. It
was thought that the reaction should therefore be fully investigated.
To explore the reaction of 1,2-dioxine and base a range of available 1,2-
dioxines (1b,c,e,f,k) were allowed to react with alkoxide and hydroxide bases under
various conditions, the results of which are summarised in Table 8 and Scheme 66.
1,2-Dioxines (1b,c,e,f,k) afforded the substituted THFs (171b,c,f), (173b,c), (174c,f)
and (175) as the sole isolable products in good combined yields. 1,2-Dioxine (1b) was
the most readily available 1,2-dioxine and so served as a good compound upon which
the effects of varying reaction conditions could be studied. Although not tabulated,
the reaction proceeded in the presence of both stoichiometric and catalytic quantities
of base with only the rate of reaction being affected. Increased concentrations of base
gave faster reaction times. When ethoxide in ethanol / THF was employed to catalyse
the reaction, the outcome was not dramatically affected although reaction times were
reduced, entries 4,7,8. Varying the reaction temperature was found to mildly affect the
reaction outcome. Lower temperatures led to an increase in the percentage of the
minor isomer (173) with the reaction times significantly increased, entries 2-3, 7-8.
Substitution on the double bond at the site of nucleophilic attack (1e, entry 8)
prevented the reaction from occurring both at ambient temperature and reflux. Thus,
when (1e) was allowed to react with lithium hydroxide, a multi-component reaction
mixture resulted and no THF products were visible in the crude 1H NMR spectra.
76
Scheme 66
OOR2R1
O
OR1
R2
O
R1
HOR2
O
OR1
R2
O
R1
HOR2
Base
O
OR1
HO
O
R1
R2R2
171b R1 = Ph, R2 = Ph171c R1 = Ph, R2 = H171f R1 = Ph, R2 = Me
1b R1 = Ph, R2 = Ph 1c R1 = Ph, R2 = H 1f R1 = Ph, R2 = Me 1k R1 = n-Pr, R2 = n-Pr
OOPh
Me1eO
OR1
R2
O
R1
HOR2
175 R1 = Ph, R2 = Me
43
256
7
1
173b R1 = Ph, R2 = Ph173c R1 = Ph, R2 = H
174c R1 = Ph, R2 = H174f R1 = Ph, R2 = Me
Table 8. The Oxa-Michael / Michael reactions of enones generated from 1,2-dioxines.
entrya dioxine time base solvent/temp oC yieldb
171 : 173 : 174 : 175
1c 1b 16 hr LiOH THF RT 50 29 - -
2d 1b 31 d LiOH THF -15 (47) (53) - -
3 1b 3 hr LiOH THF 65 (62) (38) - -
4e 1b 1 hr NaOEt CH3CN/EtOH RT 57 (78) (22) - -
5 1c 72 hr LiOH THF RT 67 (87) 7 (8) (5) -
6e 1c 1 hr NaOEt THF/EtOH RT 57 6 18 -
7e 1c 1 hr NaOEt THF/EtOH –10 (63) (16) (21)
8 1e 72 hr LiOH THF RT or 65 - - - -
9 1f 72 hr LiOH THF RT 46 - 11 22
10f 1k 16 hr NaOEt THF RT or 65 - - - -
a Reactions were performed on a 1 mmol scale with 1 equiv. of base in 5 ml solvent. b
Isolated yield, parentheses indicate ratio determined by 1H NMR. c 11% Of another
unassigned THF also isolated. Assignment of stereochemistry was not possible due to
ambiguous NOE data. d 79% Complete by 1H NMR. e A 5:1 ratio of THF: ethanol was
used. f Resulted in complete decomposition of starting material.
1,2-Dioxine (1k) did not react with lithium hydroxide at ambient temperature
due to an absence of sufficiently acidic protons α to the peroxide linkage. In the
presence of sodium ethoxide in THF/EtOH (1:1), immediate decomposition of the
1,2-dioxine was observed. Analysis of the crude reaction mixture by TLC showed that
77
the majority of products were all non-polar materials ruling out the presence of THFs
of the type previously isolated. Furthermore, when analysed by 1H NMR, the crude
reaction mixture showed resonances in the region of δ 2.0-3.0 ppm with only scattered
peaks above 3.0 ppm. This indicated that the reaction products were not similar to
those isolated from other dimerisation reactions. Separation by flash chromatography
afforded a complex mixture of non-separable non-polar oils (43%, structure
undetermined) and one polar oil (8%). Subsequent purification of the most polar
product gave a single isomer identified as THF (176) by 1D and 2D NMR data, MS
and IR. The product resulted from the ‘expected’ dimerisation to give (173k) followed
by an intramolecular aldol reaction with dehydration to give (177) then aerial
oxidation to the alcohol (176), Scheme 67. The second step of the sequence, the
intramolecular aldol cyclisation is seen in other THFs containing aliphatic ketones
vide infra. As the oxidation step was unique to this sequence, the mechanism for the
reaction was not investigated. It is necessary to note that the reaction came into
contact with oxygen for a period of three days before isolation and this may have
caused the oxidation to occur. Furthermore, due to the low yield of THF type products
the reactions of (1k) were not further investigated.
Scheme 67
OOPrnPrn NaOEt
OPrn
HOPrn
O
Prn
NaOEt
OPrn
HOPrn
Prn
OPrn
O
1k OPrn
HOPrn
O OH
Prn
176
[O]
?
173k 177
6.3 Characterisation of THFs.
The THF series (171) was assigned on the basis of COSY, ROESY, HMBC
and HMQC 2D NMR spectra. A typical ROESY spectra for (171f) (C6D6) showed
crosspeaks from protons attached to C6 (δ 3.61) and C7 (δ 2.72) with the proton at C4
(δ 4.15) as well as from protons on C7 (δ 2.72) to C2 (δ 3.98) confirming the trans
relationship of contiguous groups about the ring. The stereochemistry of the C6
hydroxyl center for THF (171f) was found by conversion of (171f) to its
corresponding acetate (178) and X-ray crystallographic structure determination,
Figure 14. The stereochemistry of the product (178) indicates that (171f) is constituted
78
from one molecule of (R)-cis-γ-hydroxyenone and one molecule of (S)-cis-γ-
hydroxyenone.
Figure 14. Molecular Structure of THF (178).
Tetrahydrofurans (173b,c) also showed characteristic splitting patterns and
crosspeaks in their 2D NMR spectra. Specifically, the ROESY spectra for (173b)
showed crosspeaks between the proton attached to C6 (δ 4.88) with C4 (δ 4.48) and
C3 (δ 3.14) as well as from protons on C7 (δ 2.84, 3.24) with C2 (δ 5.12). Further
support for the structural assignment came by conversion of (173b) to the
corresponding acetate (179) and X-ray crystallographic structure determination,
Figure 15. The stereochemistry of (179) indicates that (173b) is constituted from two
molecules of cis-γ-hydroxyenone of the same absolute stereochemistry.
79
Figure 15. Molecular structure of THF (179).
When both the hydroxyl and adjacent ketone moieties were on the same face
of the THF as in the case of (174) the molecule existed in its isomeric furanol form
(180) as evidenced by a hemiketal signal in the 13C NMR spectra δ 100-110 ppm,
Scheme 68. Only a single cyclic furanol isomer was visible in the NMR spectra for all
analogues of THF (174) synthesised. The relative stereochemistry between the
hemiketal carbon and adjacent tertiary center was determined using 2D 1H NMR and
is shown in Scheme 68. The alternative hemiketal does not form, presumably due to
steric crowding between the large phenyl or tert-butyl group with the THF ring.
The cyclisation of THF (174c) to its hemiketal allowed for the determination
of the relative stereochemistry of C6-C6a. THF (174c) was the only hemiketal
isolated that contained a stereogenic centre at C6. THF (174c) was assigned as having
R,S relative stereochemistry at C6-C6a which is different to that found for (171).
These furanol compounds were found to be very acid sensitive and although stable in
the solid state decomposed quickly when dissolved in CDCl3 due to trace acid. Their
spectra were therefore more readily obtained in either d6-acetone or d6-benzene.
80
Scheme 68
O
OPh
HO
O
Ph
MeMe
174f
O
OH
O
O
Ph
HMe
180f
Ph
Me 1
6a
3a 3
2
6
4
5
6.4 The Dimerisation of trans-γγγγ-Hydroxyenone.
The isomerisation of cis-γ-hydroxyenones (22) to trans-γ-hydroxyenone (38)
may be promoted by nucleophiles such as triethylamine and triphenylphosphine.50
This isomerisation is the basis for the reported synthesis of trans-enones from 1,2-
dioxines.50 The isomerisation of the trans-enone back to the cis-γ-hydroxyenone has
been promoted by light and heat.50,63 In the previous cyclopropanation reactions
described in Chapters 1 and 3 the cis-γ-hydroxyenone has acted as the conjugate
acceptor as shown by rate and competition studies.50,63 Additions to cis-γ-
hydroxyenones occur with attack to the least hindered side of the molecule assuming
an intramolecular hydrogen bond exists between the hydroxyl and ketone moieties.147
This is illustrated in Scheme 69. As attack to the opposite face of the molecule had
occurred in the reaction leading to the major isomers isolated from the dimerisation, it
was possible that the reaction was proceeding through the isomeric trans-γ-
hydroxyenone. To examine whether THFs could be prepared from trans-γ-
hydroxyenones, (38b,c,i,n-q) were prepared.
Scheme 69
O
OPh
Me
O
Ph
OHMe
OH
O
Ph Me
expected attackobserved attack H H
OH
O
Ph Me
O
Me
PhO
S
R
S RS
S
H
O
OPh
Me
O
Ph
OHMe
H H
RS
S
HSS
171f
181
181
81
Using the procedure developed by Avery, rearrangement of 1,2-dioxine (1b)
with Co(II)(SALEN)2 then exposure to triphenylphosphine gave (38b), Scheme 70.50
The trans-enone (38b) was unstable and so was best used immediately after isolation.
Scheme 70
PhO
PhHOOO
PhPhPh
HOO
Ph
1. Co(II)(SALEN)2 2. PPh3
1b 22b 38b
(68%)
The majority of the enones (38c,i,n-q) were prepared by allowing
glycoaldehyde to react with the appropriate stabilised keto ylide (182a-f) in refluxing
CHCl3, Scheme 71 and Table 9.63 The stabilised phosphorus ylides (182e) and (182f)
were prepared by reacting the appropriate haloalkanone with triphenylphosphine then
deprotonating with sodium carbonate.148 The ylides (182b) and (182c) were kindly
synthesised and donated by Palmer.94 The presence of ylide in the reaction mixtures
generating (38) increased the stability of the product hydroxyenones as it acted as a
proton sponge and decreased furanisation. Due to the sensitive nature of the trans-
enones, only florisil could be used as stationary phase in chromatographic purification
without significant decomposition of the trans-enone to the corresponding furan. Both
the alkyl substituted enones (38i) and (38o) could not be readily separated from TPPO
by chromatography and so were used without rigorous purification. The reaction
yields given for the THFs in Table 10 using (38i) and (38o) were therefore calculated
from the amount of glycoaldehyde dimer used. Purification to remove any unreacted
glycoaldehyde was necessary as glycoaldehyde interfered with the dimerisation
process and gave glycoaldehyde containing adducts.
82
Scheme 71
O
R1 PPh3
O
R1 OH
R2R2O
O OH
HO
+
182a R1 = Ph, R2 = H
182b R1 = 4-BrPh, R2 = H
182c R1 = But, R2 = H
182d R1 = Me, R2 = H
182e R1 = Ph, R2 = Me
182f R1 = Me, R2 = Me
38c R1 = Ph, R2 = H
38n R1 = 4-BrPh, R2 = H
38o R1 = But, R2 = H
38i R1 = Me, R2 = H
38p R1 = Ph, R2 = Me
38q R1 = Me, R2 = Me
Table 9. Synthesis of trans-Hydroxyenones.
entrya ylide enone yieldb 14
1 182a 38c 95
2 182b 38n 86
3 182c 38o -c
4 182d 38i -c
5 182e 38p 61
6 182f 38q 93
a Reactions were performed by refluxing in THF for 4 hours with 1.2 equivalents of
ylide. b Isolated yield. c trans-γ-Hydroxyenones (38o) and (38i) were not separable
from TPPO but instead were allowed to react with LiOH after filtering through
florisil.
When trans-enones (38) were allowed to react with lithium hydroxide, the
THFs (171) (173) and (174) were produced in good yield, Scheme 72 and Table 10.
Reaction times were significantly shorter than if starting from the appropriate 1,2-
dioxine due to the absence of the rate-limiting ring-opening step. The major isomer
was again (171) with all contiguous groups trans, the same as that found when
starting from 1,2-dioxine (1). All isomers were readily separable by flash
chromatography on silica gel.
83
Scheme 72
R1
O
OH
R2
LiOH
38b R1 = Ph, R2 = Ph
38c R1 = Ph, R2 = H
38n R1 = 4-BrPh, R2 = H
38o R1 = t-Bu, R2 = H
183O
OBut ButOO
O
OR1
R2
O
R1
HOR2
O
OR1
HO
O
R1
R2R2
174c R1 = Ph, R2 = H
174n R1 = 4-BrPh, R2 = H
174o R1 = But, R2 = H
173b R1 = Ph, R2 = Ph
173c R1 = Ph, R2 = H
173n R1 = 4-BrPh, R2 = H
173o R1 = But, R2 = H
O
OR1
R2
O
R1o
HOR2
171b R1 = Ph, R2 = Ph
171c R1 = Ph, R2 =H
171nR1 = 4-BrPh, R2 = H
171o R1 = But, R2 = H
43
256
7
1
Table 10. Reaction of trans-Hydroxyenones with LiOH.
entrya enone Yieldb
171 173 174
1 38b 62 (82) (18) -
2 38c 54 (90) 6 (10) -
3 38n 59 3 15
4c 38o 65 - 9 a Reactions were performed on a 1 mmol scale in THF (5 ml). b Isolated yield,
parentheses indicate ratio determined by 1H NMR. c 15% of 1,4-dioxane (183) was
also isolated.
The dimerisation of tert-butyl ketone (38o) gave a small amount of a
compound assigned as having structure (183) in addition to the expected THFs. The
compound was assigned on the basis of a molecular ion at 285 (MH+) and symmetry
seen in both the 1H and 13C NMR spectra. The relative stereochemistry of the two
groups was assigned as trans as the cis-isomer would not have been symmetrical and
both axial and equatorial groups would have been present. This would have caused
the 1H NMR to show twice the number of 1H and 13C resonances in the NMR spectra.
When 1,4-dioxane (183) was allowed to react with excess lithium hydroxide,
none of the THFs (171-174) were seen and (183) was recovered unchanged. This
indicated that (183) was not in equilibrium with (38o). The formation of the 1,4-
dioxane when starting with the tert-butyl ketone (38o) probably reflects a reduced
ability of the ketoenolate to undergo the intramolecular MIRC step of the reaction
84
sequence due to steric factors. Instead, the enolate undergoes proton exchange with
the hydroxyl and then oxa-Michael ring closure, Scheme 73.
Scheme 73
But
OOH
OOH
ButOO
But
OO
ButOO
But
O
O
But
O
But
O
38o 183
In the case of methyl ketone (38i), the reaction did not stop at THF (173i).
Further intramolecular Aldol condensation occurred, resulting in the bicyclic
compound (184), Scheme 74. Under the experimental conditions (184) underwent
slow decomposition and the best yield was obtained when the reaction was closely
followed by TLC and quenched when all starting material had been consumed.
Scheme 74
O
MeOH
38i O
OMe
HO
O
Me
O
O
Me
HO
184 (49%)
LiOH LiOH
173i
Bicyclic compound (184) showed 11 resonances in the 1H NMR and 10 13C
resonances. The IR of (184) showed a large absorption at 1651 cm-1 attributed to an
α,β-unsaturated carbonyl and a large absorption at 3435 cm-1 due to a hydroxyl group.
In the 1H NMR of (184), only a single methyl group was seen and an additional
resonance in the downfield region δ 5.96 ppm, which further indicated the presence of
a double bond. The stereochemistry of (184) was determined using 2D 1H NMR. The
two rings were assigned as being cis-fused based upon a ROESY interaction between
the aliphatic proton α to the ketone and the adjacent bridgehead proton, Figure 16.
The relative stereochemistry of the hydroxymethyl sidearm was assigned on the basis
of a ROESY interaction between the proton α to the ketone and the hydroxymethyl
protons. The THF that gives rise to (184) corresponds to (173i). The low yield may
85
indicate that the contiguous trans isomer corresponding to (171i) does form but
decomposes and is not isolable.
Figure 16. NOE crosspeaks seen in the ROESY NMR of (184) and assignment of the 1H NMR.
O
O
Me
H
HOH
H
HH
HH
H
δ 3.81
δ 2.76
δ 2.33
δ 3.63H
δ 4.00δ 4.15
H
δ 3.68
δ 5.96δ 1.99
δ 2.89
δ 2.49
2-Methyl substituted trans-enones (38p) and (38q) were expected to afford
THFs with further substitution about the ring. trans-γ-Hydroxyenone (38p) gave two
diastereomeric products (185) and (186), both with identical stereochemistry about the
THF ring but isomeric at the tertiary center α to the ring, Scheme 75.
Scheme 75a
O
PhOH
O
OPh
OH
O
PhMe O
OPh
OR1
MeMe
Me
38p185 186 R1 = H
+
O
OMe
OH
O
Me
Me
Me
188 R = Me (39%)
187 R1 = Bz b
62 : 38 (64%)
a MeOPh
O
MeOH
Me
a
38q
a Key: (a) LiOH; (b) BzCl, pyridine / CH2Cl2 (56%).
The relative stereochemistry between C3-C7 in (185) was found to be R,S as
determined by X-ray crystallography, Figure 17. The minor isomer (186) when
86
converted to its O-benzoyl derivative (187) also afforded crystals suitable for X-ray
analysis and again allowed for confirmation of assignment, Figure 18.
Figure 17. Molecular structure of (185).
Figure 18. Molecular structure of (187).
The reaction of (38q) afforded only a single isolable product (188) with
undefined stereochemistry at the methyl α to the ring. Although small singlets at δ 5.8
ppm in the crude 1H NMR spectra indicated the presence of compounds of structure
similar to (184), these could not be isolated. Thus, 2-methyl substitution in the trans-
87
enone did not significantly affect the reaction outcome as enones (38p) and (38q) still
afforded THFs with contiguous large groups trans.
In an attempt to further increase the scope of the dimerisation of γ-
hydroxyenones, the base catalysed reaction of equimolar amounts of two different
1,2-dioxines was studied. When NaOEt was added to a stirred solution of 1,2-
dioxines (1b) and (1c) in THF, a mix of homodimer and heterodimer products
resulted, Scheme 76. It was hoped that a difference in the rates of addition of the two
γ-hydroxyenones would yield useful diastereoselectivity. Although the major reaction
products were easily separable by flash chromatography, no diastereoselection was
observed and a statistical mix of homodimers (171b) and (171c) and heterodimers
(189) and (190) resulted.
Scheme 76
OOPhPh
O
OPh
O
Ph
HOPh
+OO
Ph
O
OPh
Ph
O
Ph
HO
LiOH
1b 1c
17.5%8.5%
O
OPh
Ph
O
Ph
HOO
OPh
O
Ph
HOPh
16% 13%171b 171c
189 190
6.4 Mechanism for the formation of THFs.
With a broad range of THFs produced under a range of experimental
conditions from a range of isomeric starting materials it is now possible to propose a
mechanism for their formation. From the reaction conditions and product
stereochemistry it is clear that the products are generated by an Oxa-Michael /
Michael reaction sequence. Thus, when starting from 1,2-dioxines of type (1), initial
Kornblum / DeLaMare ring-opening by the base affords the cis-γ-hydroxyenones
(22). 1,4-Addition of the hydroxide to the cis-enone followed by rotation about the
C2-C3 axis with elimination of water can establish equilibrium between the cis and
trans enone. Once equilibrium has been established, there exist two possible reaction
pathways: Pathway 1 (Scheme 69) involves the cis-enone as the initial conjugate
88
acceptor, Pathway 2, represented in Scheme 77, involves the trans-enone as the
initial conjugate acceptor.
Scheme 77
O
OR1
R2
O
R1
HOR2
192
R1
O
R2
HO
R1
O
R2
O
R1
O
R2
O
O
OR1
R2
O
R1
HOR2
191
OO 4 3
2
1
R1
R2 R2
HO
O
R1
HOH-
174
OH-
1 3822
171173
H
H
The geometry of the α,β-unsaturation can have a profound impact on the
stereoselectivity of additions to these systems by hetero-nucleophiles.149,150 The
relative stereochemistry between C5 and C6 is established in the initial hetero-
Michael addition and this is governed by the conformation of the conjugate acceptor.
When carbon nucleophiles add to cis-γ-hydroxyenones, the nucleophile adds to the
least hindered face of the enone assuming an intramolecular hydrogen bond exists
between the carbonyl and hydroxyl moieties. In the major product, the addition seems
to have occurred opposite to that expected, Scheme 69. Thus, addition to the trans-γ-
hydroxyenone is the likely cause of this reversed selectivity. Consideration must be
given to whether the cis- or trans-enone acts as the initial nucleophile. To determine
this, the intramolecular ring-closure must be examined.
The intramolecular cyclisation of enolates onto conjugate acceptors giving rise
to cyclopentanoid or tetrahydrofuranoid products has been rationalised by invoking
secondary orbital interactions.151-153 It is easiest to consider the unsubstituted case of
(38c) for which all possible cyclic transition states leading to the observed products
are drawn, Figure 19. Thus, if the nucleophile was the trans-enone, then the dominant
interaction for cyclisation proceeding through chair transition state (193a) to give
(171c) would involve the HOMO of the enolate and the LUMO of the unsaturated
ketone carbonyl.154,155 If the nucleophile was the cis-enone then a cyclic transition
state giving rise to the nucleophile and acceptor trans is not obtainable. Furthermore,
89
the only possible cyclic transition state involving the cis-enone as the nucleophile
(193d) appears highly congested. If the reaction does indeed involve cyclic transition
states then the initial nucleophile must be the trans-γ-hydroxyenone. Thus, the trans-
enone appears to be the key intermediate in this reaction sequence.
Figure 19. Cyclic transition states leading to (171-174).
O
O PhOPh OH
O
PhOPh
O
OH
O
O PhOPh OH
171c 173c
174cO
O
PhO
Ph
OH
173c
193a 193b
193c 193d
When the enone contains a stereogenic center and is racemic, as is the case when
starting from (1b), (1f) and (38b), there exists two possibilities for the initial hetero-
conjugate addition; these are the homochiral and hetereochiral combinations yielding the
two intermediates (191) and (192) respectively, Scheme 77.
The heterochiral combination of enones affords only the observed major isomer
(171b) or (171f) with all contiguous groups trans. For the homochiral combination, the
Michael ring-closure yields (173), or (174) with poor selectivity.
The discovery that the trans-enone and not the cis-enone is the key
intermediate in this reaction is significant as trans-γ-hydroxyenones may be
conveniently generated from a variety of starting materials and are appreciably more
stable than the isomeric cis-enone.
6.5 The Rearrangement of cis-γγγγ-Hydroxyenone to 1,4-Dicarbonyl.
In the beginning of this Chapter it was hypothesised that the cis-γ-
hydroxyenone to 1,4-dicarbonyl rearrangement would be catalysed by the action of
hydroxide. In none of the reactions described above was any evidence of 1,4-
dicarbonyl formation observed. In the reactions of 1,2-dioxines with nucleophiles of
90
all types, the quantity of 1,4-dicarbonyl has varied. These findings suggest that the
nature of the base can have a profound impact on the rearrangement. Hard bases such
as hydroxide and ethoxide do not promote the rearrangement, soft bases such as
triethylamine and DABCO promote the rearrangement. The lack of diketone
formation when hydroxide was the catalyst must be due to a kinetic preference for
dimerisation. Whether this kinetic preference still exists at very low concentrations of
enone is unknown. This reaction requires further investigation if a clear mechanistic
picture is to be obtained.
6.6 Conclusions
γ-Hydroxyenones undergo dimerisation to THF’s when allowed to react with
hydroxide and alkoxide bases in a variety of solvents. The major product from the
reaction has all contiguous groups trans to one another. Both cis and trans-enones
may be used as starting materials for the dimerisation. The ratios of products obtained
from the dimerisation are subtly affected by the starting material used. The Oxy-
Michael / Michael reaction described herein is interesting and possibly useful due to
the highly functionalised nature of the product THF’s.
91
Chapter 7: The Epoxidation of 1,2-Dioxines and Subsequent
Reactions of the Epoxidic Products.
7.1 Modification of the Double Bond in 1,2-Dioxines.
The synthetic utility of 3,6-dihydro-1,2-dioxines (1) as a source of cis-γ-
hydroxyenones has been discussed in previous chapters. Other chemistry not
involving cis-γ-hydroxyenone formation but utilising 1,2-dioxines in synthesis has not
received attention till now in this thesis. 3,6-Dihydro-1,2-dioxines have only two
conserved functionalities that may be easily modified, the peroxide linkage and the
double bond. As seen in Chapter 1, the double bond of (1) reacts with electrophilic
reagents and so may be halogenated, reduced and epoxidised. Both bromination and
chlorination when applied to meso-1,2-dioxines destroy the axis of symmetry due to
the anti mode of halogenation.4 However, epoxidation conserves the axis of symmetry
when applied to meso-1,2-dioxines. meso-3,6-Dihydro-1,2-dioxines may be ring-
opened using chiral Co(II) salen or β-keto-iminato complexes to furnish cis-γ-
hydroxyenones with high enantiomeric excesses.62 Since the products from the
epoxidation of the meso-3,6-dihydro-1,2-dioxines (1b,k,l,m) would again be meso it
was hypothesised that these too could be ring-opened in an asymmetric manner.
The epoxidation of bicyclic 1,2-dioxines has been used in the synthesis of
many target structures and proceeds smoothly, however, few examples of the
epoxidation of monocyclic 1,2-dioxines exist and none of the products from the
reaction with transition metals have been characterised.156-158 Preparation of a number
of meso-epoxy-1,2-dioxines would allow the asymmetric version of the transition
metal ring-opening to be applied to these new meso-epoxy-1,2-dioxines generating
useful chiral synthons. Non-symmetrical epoxy-1,2-dioxines could similarly yield
substituted 4-hydroxy-2,3-epoxy-ketones if induced to undergo a Kornblum /
DeLaMare decomposition using an appropriate base. The work in this chapter
describes the preparation of epoxy-1,2-dioxines (194) with a focus on the preparation
of meso-epoxy-1,2-dioxines which could then be desymmetrised with chiral Co(II)
complexes. Also described are the ring-opening reactions of both meso and
unsymmetrical epoxy-1,2-dioxines with Co(II)(SALEN)2 and an amine base.
92
7.2 Preparation of the Epoxy-1,2-dioxines.
1,2-Dioxines (1b,k,l,m) were chosen as starting materials as they represent
cycloalkyl, alkyl and aryl meso-1,2-dioxines and would give a range of epoxides that
could be then ring-opened asymmetrically. The unsymmetrical 1,2-dioxines (1c,e,f)
were also epoxidised as the starting materials were readily available. The epoxidation
of the 1,2-dioxines was carried out in an analogous procedure to that reported by
Herz.43 Thus, when (1) was allowed to react with m-CPBA, the sole isolable products
were epoxy-1,2-dioxines (194) and (195) with moderate to good diastereoselectivity
in excellent yield, Table 11, Scheme 78.
Scheme 78
OOR2R1 m-CPBA OO
R2R1
R3 R3O
OOR2R1
R3O
1b R1 = R2 = Ph, R3 = H1c R1 = Ph, R2 = H, R3 = H1e R1 = Ph, R2 = H, R3 = Me1f R1 = Ph, R2 = Me, R3 = H1k R1 = R2 = n-Pr, R3 = H1l R1 = R2 = c-C6H11, R3 = H1m R1 = R2 = i-Pr, R3 = H
1
5a
5
4 3
2
1a
194 195
Table 11. Epoxidation of 3,6-dihydro-1,2-dioxines using m-CPBA.
entrya 1,2-dioxine time (days) 194 : 195b Yieldc
1 1b 14d 100:0 83
2 1c 10 84:16 74
3 1e 2 93:7 92
4 1f 7 84:16 93
5 1k 1 63:37 85
6e 1l 1 77:23 84
7 1m 3 69:31 51 a Reactions were typically performed on a 1 mmol scale with 1.2 equiv. of m-CPBA
in CH2Cl2 (5 ml). b Ratio measured using NMR on crude material c Combined isolated
yield. d 94% complete by 1H NMR. e 1.8 equiv. of m-CPBA used.
93
The major isomer corresponded to reaction of the peroxy acid on the least
hindered side of the 1,2-dioxine and was termed the trans isomer. Diastereoselectivity
was greatest for the 3,6-diphenyl dioxine (1b) where none of the all cis-isomer (178)
was detectable by 1H NMR or TLC although the reaction proceeded only sluggishly,
entry 1. Substitution at the 4-position in the parent 1,2-dioxine (1e) was found to
increase the observed diasteroselectivity, compare entries 2 and 3.
The identity of the major trans-isomer (194) was determined by 1H NMR.
Typically, the protons attached to C1a and C2 showed no or very little coupling due to
an approximate 90o dihedral angle and therefore appeared as broadened singlets as in
(194b) or doublets where not symmetrical, (194c) and (194f). The minor isomer (195)
with all groups cis typically showed a larger coupling between the C1a and C2
protons causing the signals to appear as non-first order multiplets. All isomers showed
the expected number and type of resonances in their 13C NMR attributable to epoxidic
carbons (50-60 ppm) and carbons α- to the peroxide group (70-85 ppm) as well as
substitution specific carbons. The IR spectra showed no absorbances above 1600 cm-1
other than those due to C-H bonds at ≈ 3000 cm-1. Both isomers were readily
separable by flash chromatography with relative polarity alone giving useful
indications on the stereochemical identity of the isomers. The all cis isomers were
without exception less polar than the trans isomers due to a steric shielding of the
polar epoxide group by the non-polar R-groups. Both isomers were considerably more
stable than their 3,6-dihydro counterparts (1) and could be stored neat at room
temperature for several months without decomposition.
7.3 Ring-opening of Epoxy-dioxines (194) and (195).
We next examined the ring-opening of epoxy-1,2-dioxines (194) and (195)
using either a mild amine base or transition metal catalyst, the results of which are
summarised in Scheme 79 and Table 12. Symmetrical epoxides were ring-opened
using Co(II)(SALEN)2 (method b) and unsymmetrical epoxides using triethylamine
(method a) so that no problems associated with regioselectivity were encountered.
Use of an appropriate method resulted in the corresponding 4-hydroxy-2,3-epoxy-
ketones (196) or (197) being formed in excellent yields.
94
Scheme 79
OOR2R1
O
OOR2R1
O
O
R2R1
O
OH
O
R2R1
197
O
OH
NEt3 (method a)or
Co(II) (method b)R3 R3
NEt3 (method a)or
Co(II) (method b)
195f, R1 = Ph, R2 = Me195l, R1 = c-C6H11, R2 = c-C6H11
194b R1 = R2 = Ph, R3 = H194c R1 = Ph, R2 = H, R3 = H194e R1 = Ph, R2 = H, R3 = Me194f R1 = Ph, R2 = Me, R3 = H194k R1 = R2 = n-Pr, R3 = H194l R1 = R2 = c-C6H11, R3 = H194m R1 = R2 = i-Pr, R3 = H
196
Table 12. Ring-opening of (194) or (195) using NEt3 (method a) or Co(II)(SALEN)2
(method b) affording 2,3-epoxy-ketones (196) and (197).
entrya epoxide method yieldb
196 / 197
1 194b a 100
2 194b b 98
3 194c a 86
4 194e a 84
5 194f a 100
6 194k b 96
7 194l b 95
8 194m b 89
9 195f a 83
10 195l b 77 a Reactions were typically performed on a 40 mg scale with 1 equivalent of
triethylamine or 2.5% w/w of Co(II)(SALEN)2. b Isolated yield by silica gel
chromatography.
The mechanisms for the ring-openings of these epoxy-1,2-dioxines (194) and
(195) are analogous to the ring-opening reactions of 3,6-dihydro-1,2-dioxines (1),
95
Scheme 80. Thus, in the case of Co(II) catalysis, single electron transfer from the
cobalt to oxygen affords an oxygen centered radical which then undergoes a 1,5-
hydrogen atom abstraction regenerating the Co(II) catalyst.42,44,62 Base catalysis
involves the removal of the most acidic proton α to the peroxide linkage then
rearrangement through cleavage of the peroxide linkage to afford the 4-hydroxy-2,3-
epoxy-ketones.25,49,159 The presence of an α-phenyl group significantly increased the
acidity of the benzylic proton and caused the reaction to proceed regioselectively, thus
(194c,e,f) afforded (196c,e,f), entries 3-5 and (195f) gave (197f), entry 9, with no
evidence of removal of the alkyl proton by examination of the crude NMR.
Scheme 80
OOR1R
O
HB
RO
O
OH
R1
OOR1R
O
OOR1R
O
RO
O
OH
R1
Co(III)
H
Co(II) Co(II)
194 / 195
194 / 195
196 / 197
196 / 197
The characterisation of the product hydroxy ketones by NMR was complicated
as the products (196) and (197) existed in both their acyclic and cis and trans cyclic
furanol forms (198-201), Scheme 81. 2D 1H and 13C NMR was used to assign the
resonances in the 1D 1H spectra from which isomeric ratios could be determined. The
furanol forms showed resonances at ≈ δ 100 ppm in their 13C NMR spectra consistent
with a hemiketal carbon, while phenyl substituted hydroxy ketones showed
resonances at ≈ δ 200 ppm for the aryl ketone. Long range 1H–13C correlation
spectroscopy (HMBC) was used to link resonances in the 1D 1H with the identifying 13C signals. It was not possible to assign all aromatic peaks in the 13C spectra to a
specific anomer for all furanols. A lack of through-space interactions in the 2D 1H
NMR of the furanol pairs (198/199) and (200/201) made assignment of the anomeric
carbon difficult, thus, although all signals could be assigned to an anomer the relative
96
configuration of the anomers could not be determined. This was a problem seen also
in the unsaturated furanols described in Chapter 3.
The nujol mull IR spectra of the 4-hydroxy-2,3-epoxy-ketones were used to
determine whether the epoxy-ketone existed in its cyclic or acyclic form when neat.
Typically, phenyl substituted epoxy-ketones existed in their acyclic form when
crystalline as they showed an aryl-carbonyl stretching adsorption at 1670 - 80 cm-1
and as an equilibrium mixture in solution. The alkyl substituted epoxy-ketones existed
solely in their cyclic forms when neat and in solution as could be seen by an absence
of the carbonyl absorption. Specific population ratios for each of the epoxy ketones
measured in CDCl3 are given in Scheme 81 and Table 13. X-ray crystallography was
used to confirm the identity of the epoxy-ketone (196f), validating the assignment of
structure in the solid state for the series of epoxy-ketones (196) and the trans-
relationship between the epoxidic oxygen and R-groups in the parent epoxy-1,2-
dioxine (194f), Figure 20.
97
Scheme 81
197f R1 = Ph, R2 = Me197l R1 = c-C6H11, R2 = c-C6H11
196b R1 = R2 = Ph, R3 = H196c R1 = Ph, R2 = H, R3 = H196e R1 = Ph, R2 = H, R3 = Me196f R1 = Ph, R2 = Me, R3 = H196kR1 = R2 = n-Pr, R3 = H196l R1 = R2 = c-C6H11, R3 = H196m R1 = R2 = i-Pr, R3 = H
O
R2R1
O
OHOHO
R1R2
O
OR1
HOR2
OR3R3 R3
O
R2R1
O
OHOHO
R1R2
O
OR1
HOR2
O200 201
198 199
Table 13. Isomeric ratios of 4-hydroxy-2,3-epoxy-ketones measured when neat and
dissolved in CDCl3.
entry ketone neata additiveb ratioc
196 : [198 : 199]
1 196b 196b - 57 : [37 : 6]
2 196c oild - 39 : [55 : 6] 3 196e 198e / 199e - 32 : [55 : 8] 4 196f 196f - 41 : [51 : 8] 5c 196f 0.7 equiv NEt3 39 : [55 : 6] 6 196f 1.2 equiv NEt3 36 : [60 : 4] 7 196f 2.5 equiv NEt3 35 : [61 : 4] 8 196f 0.5 equiv DABCO 27 : [68 : 5] 9 196k 198k / 199k - 0 : [79 : 21]
10 196l 198l / 199l - 0 : [78 : 22] 11 196m 198m / 199m - 0 : [70 : 30] 12 197f 197f - 26 : [61 : 13]e 13 197l 200l / 201l - 0 : [77 : 23]e
a Refers to which isomeric form the 4-hydroxy-2,3-epoxy-ketone exists in when neat.
Determined by IR. b Additive refers to the addition of compound to 0.7 ml CDCl3,
equiv. referenced to quantity of compound. c Ratio determined by 1H NMR by
dissolving in CDCl3 and allowing to equilibrate for 1 hour before integrating peak
height. Anomers (198) and (199) could not be unambiguously assigned. d Could not
be determined. e Ratio of 197 : 200 : 201.
98
Figure 20. Molecular structure of epoxide (196f).
The ratio of cyclic furanols to open chain ketone was sensitive to the presence
of amine bases. The addition of triethylamine or DABCO to a solution of (196f)
decreased the amount of open chain ketone in favour of the cyclic furanols, entries 4-
8, Table 13. The observed ratio changes were sensitive to the amount of amine present
in solution, however a plateau was reached and no further change was observed after
the addition of 2.5 equivalents of triethylamine. The larger shift in ratio seen in the
presence of DABCO is probably due to the increased basicity of DABCO compared
to triethylamine, however a systematic study of different bases was not undertaken.
7.4 Asymmetric Ring-opening of Epoxy-1,2-dioxines.
One of the stated aims in this work was to develop new substrates for the
asymmetric ring-opening with chiral Co(II)Salen complexes. The asymmetric version
of these Co(II) catalysed ring-opening reactions were carried out by another member
of the research group with supplied material and have since been reported.80,86 The
optimised conditions for the ring-opening of (194b) were found to be with a catalyst
loading of 7.5% at 20°C in THF and gave an ee of up to 84%, Scheme 82.
99
Scheme 82
OOPhPh
194bO
O
PhPh
196bO
OH
quantitative
ee = 84%
OCo
N
O
N
Ph Ph
O
RO
O
OR
R = (-)-bornoxy
7.5 Antimalarial and Antifungal Properties of Epoxy-1,2-dioxines.
As seen in Chapter 1, the natural products Artemisinin and Yingzhaosu A-C
show marked antimalarial and antifungal activity and are under intense study as
promising clinical agents for the treatment of malaria infection. As the peroxide bond
gives the molecules their potent activity, the synthesis and evaluation of structurally
simpler endocyclic peroxides is a worthwhile endeavor.160 The epoxy-1,2-dioxines
prepared in this study had potential for activity against the malaria causing parasite
due to the presence of the peroxide linkage. The presence of the epoxide also gives an
oxygen atom in a spatially similar position to the 4-oxygen atom as that found in the
known antimalarial 1,2,4-trioxanes.
When several of the epoxy-1,2-dioxines were tested in collaboration with
McCreadie and Tilly, marked activity against both the malaria causing parasite P.
falciparum and the fungus Aspergilus Niger was seen. Selected results for the
antimalarial activity are shown in Table 14. The 2-alkyl substituted 1,2-dioxines
showed better in vitro activity against P. falciparum than the aryl substituted 1,2-
dioxines, however, a full discussion of the bioactivity and structure/activity
relationships of the compounds derived from this work is beyond the scope of this
thesis.
100
Table 14. Antimalarial Activity of Selected Epoxides.
Entry Compound IC50 (μM) Hemolysis
1 Artemisinin 0.01 4
2 1b 6.0 4
3 1f >10 32
4 1j 3.2 100
5 1l 4.2 100
6 194b >10 5
7 194f >10 2
8 194j >10 2
9 194l 0.5 6
10 195l 0.32 5
7.6 Conclusions.
Epoxy-1,2-dioxines (194) can be readily prepared from 3,6-dihydro-1,2-
dioxines (1) in high yield and good to excellent de. Exposure of these epoxy-1,2-
dioxines to either triethylamine or Co(II) complexes allowed for the preparation of 4-
hydroxy-2,3-epoxy-ketones (196 / 197) in excellent yields. These epoxy-ketones
existed in their acyclic and cyclic furanol forms in solution, the ratios determinable by
2D NMR experiments. The meso-epoxy-1,2-dioxines could also be ring-opened in an
asymmetric fashion when allowed to react with selected Co(II) catalysts. Some of the
epoxidic dioxine products showed antimalarial / antifungal activity.
7.7 Conclusions and Future Work.
Several new reactions and synthetic methodologies starting with 1,2-dioxines
have been described. These processes include both modification of the alkene portion
of the 1,2-dioxine and also reaction of the peroxide linkage within the 1,2-dioxine.
Using the intermediacy of the cis-γ-hydroxyenone, 1,2-dioxines were converted to a
range of ring structures; namely furans, cyclopropanes and cyclopentenes. A summary
of these is seen in Scheme 81.
101
Scheme 81
OOR2R1
OHO
O
R1
R2
O
R1
R2
LiOH
m-CPBA
OOR2R1
O
OHOR2R1
O
Co(II) or
NEt3
LiBr,ylide
CO2RR1
OR2
OH
R1
CO2R
R1
HO
R1R2
CO2RTFA
For R1 = R2
Co(II)OHOR2R1
R2
CO2RR2
OHCO2R
O
R1
ylideylide
R1 = H
1
LHMDS
This body of work has substantially increased the utility of the 1,2-dioxine.
Future work should focus on an expansion of the types of nucleophiles that can add to
cis-γ-hydroxyenones. Ideally, nucleophiles that are weakly basic enough so that they
can rearrange the 1,2-dioxine yet nucleophillic enough such that they can still add to
the cis-γ-hydroxyenone. Nucleophiles that contain functionality that can further react
with the γ-hydroxyl group after addition of the nucleophile will allow interesting
functionalities to be synthesised. Further extensions to the Oxa-Michael / Michael
reaction (THF synthesis, Chapter 6) using 1,2-dioxines and other Michael acceptors
could be examined. The development of this reaction would facilitate the use of the
1,2-dioxine in synthesis.
102
Chapter 8: Experimental
8.1 General Experimental.
Dichloromethane was dried from P2O5 and freshly distilled before use. THF and
diethyl ether were dried using benzophenone ketyl and freshly distilled before use. All
organic extracts were dried over anhydrous sodium sulphate.
Flash chromatography was performed using Merck silica gel 60 (230 – 400 mesh)
unless otherwise stated. Thin Layer Chromatography was performed using aluminum
backed sheets of silica gel F254 obtained from Merck. . Florisil® was obtained from
the Aldrich chemical company.
Melting points were determined using a Reichert Thermovar Kofler instrument and
are uncorrected.
Infrared spectra were recorded using an Perkin-Elmer BX FT-IR system.
Microanalysis were carried out at the University of Otago, New Zealand.
Accurate mass determination was performed at the University of Tasmania using
Electron Impact or Liquid Spray Ionisation techniques. Mass spectra were obtained
using a Vacuum Generated ZAB 2HF mass spectrometer operating at 70 eV, using
Electron Impact ionisation.
X-ray crystallography of compounds (119b, 119c) was performed using a Rigaku
AFC7R by Dr E. R. T. Tiekink, Adelaide University. X-ray crystallography of
compounds (178), (179), (185), (187), and (196f) were conducted by Dr E. R. T.
Tiekink at the National University of Singapore. X-ray crystallography of compounds
(158b) (164) was performed using a GDF: Nonius CCD by Dr G. D. Fallon, Monash
University, Victoria. 1H and 13C NMR spectra were recorded in CDCl3 unless specified on either a Varian
Gemini 2000 (200 MHz or 300 MHz) or Varian INOVA (600 MHz) instrument with
TMS (0 ppm) and CDCl3 (77.0 ppm) as internal standards with shifts reported in parts
per million (ppm). 1H NMR multiplicities are given the abbreviations: singlet (s),
doublet (d), triplet (t), quartet (q), pentet (pent), multiplet (m), and broad (br) denoting
broadened signals. 31P NMR chemical shifts were referenced to 85% aqueous H3PO4
(external) in CDCl3. ABX spectra were analysed by use of the effective Larmor
frequencies method using the NMR program written and kindly supplied by Dr G. T.
Crisp, University of Adelaide.
103
All yields refer to isolated material judged to be greater than 95% pure by TLC and
NMR spectroscopy.
Cyclopropane (82b) was kindly synthesised and donated for use by Dr Tom Avery
using the protocol outlined in Chapter 4. Cyclopropane (82f) was kindly synthesised
and donated for use by Ms Julie Culbert using the protocol outlined in Chapter 4. The
two stabilised keto ylides (182b) and (182c) were kindly synthesised and donated for
use by Dr Francine Palmer.
The following compounds were purchased from Aldrich chemical company and were
used without further purification: N,N’-bis(salicylidene)-ethylenediaminocobalt(II)
(24), N,N’-bis(salicylidene)-ethylenediaminocobalt(II) hydrate (24).H2O, benzyl
(triphenylphosphoranylidene)acetate (34a), tert-butyl
(triphenylphosphoranylidene)acetate (34c), Rose Bengal bis(triethylammonium)salt,
(R,R)-N,N’-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diaminocobalt(II) (39),
(1E,3E)-1,4-diphenyl-1,3-butadiene (61b), (2E,4E)-2,4-hexadiene-1-ol (61h) and (E)-
1,3-pentadiene (61i).
104
8.2 Compounds Described in Chapter 2.
General Procedure for the Synthesis of 1,3-Butadienes (61c-k). To a stirred
solution of alkyltriphenylphosphonium halide (60a-e) (10 mmol) dissolved in ether
(100 ml) under an atmosphere of N2 was added potassium butoxide (11 mmol). The
resulting brightly colored (yellow-red) solution was stirred for 30 minutes then the
appropriate aldehyde or ketone (59a-e) (10 mmol) was slowly added over 30 minutes.
The solution was stirred for 16 hours then hexane (100 ml) was added. The solution
was filtered through a pad of silica then concentrated in vacuo. The crude butadienes
were purified by squat chromatography (hexane).
General Procedure for the Preparation of 1,2-Dioxines (1) from 1,3-Butadienes
(61b-k). A solution of 1,3-butadiene (61b-k) (3.0 g) and rose bengal
bis(triethylammonium) salt (100 mg) dissolved in CH2Cl2 (100 ml) in a water-
jacketed flask cooled to 0°C was irradiated with 3 × 500 W tungsten lamps for a
period of 6 hours. The solution was then concentrated in vacuo and the product
subjected to flash chromatography to yield the product 1,2-dioxine (1) and any
unreacted starting diene, which could be recycled.
(±±±±) (R,S)-3,6-Diphenyl-3,6-dihydro-1,2-dioxine (1b).50,77 Colourless solid; Yield
71%; mp 83-84 °C; Lit 82-83 °C.
3-Phenyl-3,6-dihydro-1,2-dioxine (1c).50,77 Colourless oil; Yield 40%; Rf 0.60 (90:10
hexane/ethyl acetate).
4-Methyl-3-phenyl-3,6-dihydro-1,2-dioxine (1d). Irradiation of (E)-2-methyl-1-
phenyl-1,3-butadiene (5.0 g, 28 mmol) as per the standard procedure gave the starting
diene (1.04 g, 21%) and 1,2-dioxine (1d) (1.08 g, 18%); Rf 0.45 (9:1 hexane/ethyl
acetate); IR (neat) 3031, 2883, 1679, 1492, 1454 cm-1; 1H NMR (200 MHz) δ 1.58 (d,
J = 0.6 Hz, 3H), 4.55-4.74 (m, 2H), 5.32 (s, 1H), 5.87 (br s, 1H), 7.30-7.60 (m, 5H); 13C NMR (50 MHz) δ 18.7, 70.0, 84.4, 119.8, 128.4, 128.8, 129.2, 133.4, 136.4; MS
(EI) m/z (%): 176 (M+) (5), 158 (15), 144 (100), 129 (50); HRMS calcd for C11H12O2:
176.0837, found: 176.0831.
105
5-Methyl-3-phenyl-3,6-dihydro-1,2-dioxine (1e).78 Colourless oil; Yield 47%; Rf
0.60 (90:10 hexane/ethyl acetate).
(±±±±) (3R,6R) 3-Methyl-6-phenyl-3,6-dihydro-1,2-dioxine (1f).50,77,79 Colourless oil;
Yield 74%; Rf 0.60 (90:10 hexane/ethyl acetate).
3-Heptyl-3,6-dihydro-1,2-dioxine (1g). Irradiation of (3E/Z)-1,3-undecadiene (930
mg, 6.1 mmol) as per the standard procedure gave unreacted starting diene (317 mg,
34%) and (1g) (334 mg, 30%); IR (neat) 3043, 2927, 1466, 1378, 1037 cm-1; 1H NMR
(300 MHz) δ 0.86 (t, J = 6.6 Hz, 3H), 1.20-1.70 (m, 12H), 4.40-4.46 (m, 1H), 4.58-
4.60 (m, 2H), 5.85-6.0 (m, 2H); 13C NMR (50 MHz) δ 14.0, 22.5, 25.1, 29.0, 29.4,
31.7, 32.6, 69.7, 78.6, 123.8, 128.1; MS (EI) m/z (%): 166 (M+-H2O, 3), 153 (20), 97
(20), 41 (100). HRMS calcd for (M+Na+, ESI) C11H20O2: 207.1360; found: 207.1358.
(±±±±) (3R,6S)-3-(Hydroxymethyl)-6-methyl-3,6-dihydro-1,2-dioxine (1h).18,19
Colourless oil; Yield 72%; Rf 0.40 (60:40 hexane/ethyl acetate).
3-Methyl-3,6-dihydro-1,2-dioxine (1i).77 Colourless oil; Yield 27%; Purified by
bulb-bulb distillation at 15 mmHg (80°C bath temperature).
3-Cyclohexyl-3,6-dihydro-1,2-dioxine (1j). Irradiation of (E/Z)-1-cyclohexyl-1,3-
butadiene (61j) (3.10 g, 22.7 mmol) as per the standard procedure afforded (1j) as a
colourless oil (2.10 g, 55%); Rf 0.62 (1:1 hexane/CH2Cl2); IR (neat): 1449, 1043, 975,
698 cm-1; 1H NMR (300 MHz) δ 5.99-5.98 (m, 2H), 4-63-4.57 (m, 1H), 4.48-4.42 (m,
1H), 4.37-4.33 (m, 1H), 1.89-1.82 (m, 1H), 1.78-1.58 (m, 5H), 1.30-1.04 (m, 5H); 13C
NMR (75 MHz) δ 26.0, 26.1, 26.4, 28.6, 28.7, 41.1, 69.9, 82.6, 124.4, 126.7; MS (EI)
m/z (%): 168 (M+, 4), 83 (100), 69 (39), 55 (96), 41 (62). HRMS calcd for C10H16O2:
168.1148; found: 168.1150.�
(±±±±) (3R,6S)-3,6-Dipropyl-3,6-dihydro-1,2-dioxine (1k). Irradiation of 4,6-decadiene
(3.51g, 25.5 mmol) under the standard conditions afforded (1k) as a colourless oil
(2.64 g, 61%); IR (neat) 2960, 1465, 1378, 1066 cm-1; 1H NMR (300 MHz) δ 0.93 (t,
J = 7.2 Hz, 6H), 1.23-1.71 (m, 8H), 4.44-4.48 (dd, J = 8.4, 2.7 Hz, 2H), 5.87 (s, 2H); 13C NMR (75 MHz) δ 13.9, 18.6, 35.0, 78.1, 127.8.
106
8.3 Compounds Described in Chapter 3.
General Procedure for the Cobalt(II) Catalysed Rearrangement of 1,2-Dioxines.
To a stirred solution of Co (II) catalyst (24) or (39) (1 mg) dissolved in CDCl3 was
added 1,2-dioxine (20 mg). The consumption of 1,2-dioxine was monitored using 1H
NMR and TLC and when complete, the solution was allowed to attain ambient
temperature and equilibrate for 1 hour before isomeric ratios were measured. The
mixtures could be stored for a short period of time (1-2 days, -15°C), however, some
decomposition occurred over this time. In all cases, dehydration to furan occurred
after prolonged storage but could be slowed if trace acid was removed from the
chloroform by passage through a short Al2O3 column before use.
(Z)-4-Hydroxy-1-phenyl-2-buten-1-one (22c).50 1H NMR (600 MHz) δ 3.15 (br s,
1H), 4.60 (dd, J = 5.1, 1.5 Hz, 1H), 6.63 (dt, J = 12.0, 5.1 Hz, 1H), 7.01 (dt, J = 12.0,
1.5 Hz, 1H), 7.25-7.29 (m, 3H), 7.97-8.00 (m, 2H); 13C NMR (150 MHz) δ 61.1,
123.7, 128.5, 128.7, 133.2, 137.7, 147.8, 191.9.
5-Phenyl-2,5-dihydro-2-furanol (67c) / (68c). Mixture of two anomers; 1H NMR
(600 MHz) δ 3.09-3.09 (m, D2O exch., 1H), 3.20-3.28 (m, D2O exch., 1H), 5.71 (br d,
J = 1.2 Hz, 1H), 5.92-5.94 (m, 2H), 5.96 (ddd, J = 6.0, 2.4, 1.2 Hz, 1H), 6.17-6.21 (m,
3H), 6.30 (br s, 1H), 7.25-7.39 (m, 10H); 13C NMR (150 MHz, partial) δ 86.7, 87.4,
103.2, 103.4.
(±±±±) (R,R)-4-Methyl-5-phenyl-2,5-dihydro-2-furanol (67d). 1H NMR (600 MHz) δ
1.61 (br s, 3H), 2.84 (br d, J = 8.4 Hz, exch. D2O, 1H), 5.64 (m, 1H), 5.66 (m, 1H),
6.26 (dd, J = 4.2, 8.4 Hz, 1H), 7.21-7.37 (m, 5H); 13C NMR (150 MHz) δ 12.0, 89.2,
103.1, 122.5, 126.7, 128.2, 129.1, 139.3, 145.1.
(±±±±) (R,S)-4-Methyl-5-phenyl-2,5-dihydro-2-furanol (68d). 1H NMR (600 MHz) δ
1.61 (br s, 3H), 3.03 (br d, J = 7.1 Hz, exch D2O, 1H), 5.40 (dd, J = 1.0, 1.0 Hz, 1H),
5.60 (m, 1H), 6.12 (dq, J = 7.1, 1.2 Hz, 1H), 7.21-7.37 (m, 5H); 13C NMR (150 MHz)
δ 12.2, 89.9, 102.8, 122.0, 122.1, 126.9, 128.1, 139.8, 144.6. IR (neat, mixture) 3375,
107
2918, 1670 (weak), 1454, 1118, 1007 cm-1. MS (GCQ, mixture (67d)/(68d) m/z (%):
175 (trace, M+-H), 158 (100, M+-H2O).
(Z)-4-Hydroxy-3-methyl-1-phenyl-2-buten-1-one (22e). 1H NMR (200 MHz) δ 2.12
(d, J = 1.2 Hz, 3H), 3.60-4.40 (br s, 1H, OH), 4.38 (br s, 2H), 6.89 (s, 1H), 7.1-7.6 (m,
3H), 7.91-7.98 (m, 2H); 13C NMR (50 MHz) δ 24.2, 63.6, 122.2, 128.4, 128.5, 132.8,
138.2, 161.4, 191.9.
3-Methyl-2-phenyl-2,5-dihydro-2-furanol (65e). 1H NMR (200 MHz) δ 1.80 (d, J =
1.8 Hz, 3H), 4.59 (d, J = 13.5 Hz, 1H), 4.75 (d, J = 13.5 Hz, 1H), 5.60 (q, J = 1.2 Hz,
1H), 7.10-7.60 (m, 5H).
3-Methyl-5-phenyl-2,5-dihydro-2-furanol (67e) / (68e). Major anomer: 1H NMR
(600 MHz) δ 1.83 (s, 3H), 3.40 (br s, exch. D2O, 1H), 5.63 (br s, 1H), 5.73 (m, 1H),
5.91 (br s, 1H), 7.22-7.40 (m, 5H); 13C NMR (150 MHz) δ 11.7, 86.2, 104.6, 136.6,
141.1 (4 obscured aromatic). Minor anomer: 1H NMR (600 MHz) δ 1.83 (s, 3H), 3.39
(br s, exch. D2O, 1H,), 5.73 (m, 1H), 5.85 (m, 1H), 6.02 (d, J = 2.6 Hz, 1H), 7.22-7.40
(m, 5H); 13C NMR (150 MHz) δ 11.7, 86.6, 104.9, 136.9, 140.7 (4 obscured
aromatics).
(Z)-4-Hydroxy-1-phenyl-3-penten-2-one (22f). 1H NMR (600 MHz) δ 1.40 (d, J =
6.6 Hz, 3H), 3.50 (br s, exch. D2O, 1H), 4.88 (dddq, J = 6.6, 6.6, 3.6, 1.2, 1H), 6.43
(dd, J = 12.0, 6.6 Hz, 1H), 6.92 (dd, J = 12.0, 1.2 Hz, 1H), 7.20-7.45 (m, 5H); 13C
NMR (150 MHz) δ 22.2, 64.7, 124.5, 131.0, 137.5, 152.8, 192.4, 1 obscured
aromatic.
(Z)-4-Hydroxy-5-phenyl-3-penten-2-one (64f). 1H NMR (600 MHz) δ 2.28 (s, 3H),
3.85 (br s, exch. D20, 1H), 5.92 (dd, J = 6.0, 4.2 Hz, 1H), 6.24 (d, J = 12 Hz, 1H),
6.30 (dd, J = 12.0, 6.0 Hz, 1H), 7.2-7.6 (m, 5H); 13C NMR (150 MHz) δ 31.3, 70.1,
126.4, 133.0, 124-135 4 aromatic carbons, 200.3.
2-Methyl-5-phenyl-2,5-dihydro-2-furanol (67f) / (68f). Major anomer: 1H NMR
(600 MHz) δ 1.65 (s, 3H), 2.74 (br s, exch. D2O, 1H), 5.72 (dd, J = 1.8, 1.8 Hz, 1H),
5.94 (dd, J = 6.0, 1.8 Hz, 1H), 6.08 (dd, J = 6.0, 1.8 Hz, 1H), 7.20-7.60 (m, 5H); 13C
108
NMR (150 MHz) δ 26.3, 86.4, 109.9, 126.3, 127.9, 128.5, 131.2, 140.6. Minor
Anomer: 1H NMR (600 MHz) δ 1.72 (s, 3H), 2.79 (br s, exch. D2O, 1H), 5.87 (br s,
1H), 5.96 (dd, J = 6.0, 2.4 Hz, 1H), 6.06 (dd, J = 6.0, 1.2 Hz, 1H), 7.20-7.60 (m, 5H); 13C NMR (150 MHz) δ 26.8, 86.2, 109.9, 126.4, 126.4, 128.0, 128.5, 131.2, 133.2,
139.9.
(Z)-1-Hydroxy-2-undecen-4-one (22g). 1H NMR (600 MHz) δ 0.87 (t, J = 6.9 Hz,
3H), 1.24-1.53 (m, 10H), 2.51 (t, J = 7.2 Hz, 2H), 4.48 (br s, 2H), 6.26 (dt, J = 12.0,
1.8 Hz, 1H), 6.34 (dt, J = 12.0, 5.4 Hz, 1H); 13C NMR (150 MHz, partial) δ 43.9,
60.8, 127.1, 202.8
2-Heptyl-2,5-dihydro-2-furanol (65g). 1H NMR (600 MHz, partial) δ 0.87 (t, J = 6.9
Hz, 3H), 1.24-1.64 (m, 12H), 4.54 (ddd, J = 14.4, 1.8, 1.8 Hz, 1H), 4.72 (ddd, J =
14.4, 2.4, 1.8 Hz, 1H), 5.80 (ddd, J = 6.0, 2.4, 1.8 Hz, 1H), 6.12 (ddd, J = 6.0, 1.8, 1.8
Hz, 1H); 13C NMR (150 MHz, partial) δ 73.8, 129.9, 130.0
5-Heptyl-2,5-dihydro-2-furanol (67g) / (68g). Major anomer: 1H NMR (600 MHz) δ
0.87 (t, J = 6.9 Hz, 3H), 1.24-1.50 (m, 10H), 1.60 (dt, J = 7.2 Hz, 2H), 2.91 (br d, J =
6.6 Hz, exch. D2O, 1H), 4.67 (dt, J = 4.2, 1.8 Hz, 1H), 5.83 (ddd, J = 6.0, 2.1, 1.2 Hz,
1H), 6.00 (br d, J = 6.6 Hz, 1H), 6.12-6.14 (m, 1H); 13C NMR (150 MHz, partial) δ
36.9, 85.6, 102.8, 127.7, 135.2. Minor Anomer: 1H NMR (600 MHz) δ 0.87 (t, J = 6.9
Hz, 3H), 1.24-1.45 (m, 10H), 1.52-1.56 (m, 2H), 4.94-4.97 (m, 1H), 5.84 (ddd, J =
6.0, 2.4, 1.2 Hz, 1H), 6.07 (br s, 1H), 6.12-6.14 (m, 1H); 13C NMR (150 MHz, partial)
δ 35.3, 84.9, 102.6, 127.7, 135.2.
(Z)-5,6-Dihydroxy-3-hexen-2-one (64h). 1H NMR (600) δ 2.27 (s, 3H), 2-obscured
aliphatic protons, 4.81-4.84 (m, 1H), 6.17 (dd, J = 11.4, 6.6 Hz, 1H), 6.32 (dd, 11.4,
1.8 Hz, 1H); 13C NMR (150) δ 31.2, 65.3, 68.0, 128.5, 147.1, 200.4.
(±±±±) (2S,5S)-5-(Hydroxymethyl)-2-methyl-2,5-dihydro-2-furanol (67h). 1H NMR
(600) δ 1.60 (s, 3H), 3.54 (dd, J = 11.4, 5.4 Hz, 1H), 3.71 (ddd, J = 11.4, 2.4, 2.4 Hz,
1H), 4.98-5.00 (m, 1H), 5.93 (obscured, 1H), 5.96 (dd, J = 6.0, 1.2 Hz, 1H); 13C NMR
(150) δ 26.9, 64.6, 85.3, 109.7, 129.6, 133.0.
109
(±±±±) (2S,5R)-5-(Hydroxymethyl)-2-methyl-2,5-dihydro-2-furanol (68h). 1H NMR
(600) δ 1.58 (s, 3H), 3.37 (br s, exch. D2O, 1H), 3.57 (dd, J = 12.0, 2.4 1H), 3.78 (dd,
12.0, 3.0 Hz, 1H), 4.32 (br s, exch. D2O, 1H), 4.82-4.84 (m, 1H), 5.87 (dd, J = 6.0, 1.8
Hz, 1H), 5.92 (dd, J = 6.0, 2.4 Hz, 1H); 13C NMR (150) δ 25.2, 62.2, 85.0, 106.1,
128.7, 133.4.
General Procedure for the Derivitisation of cis-γγγγ-Hydroxyenones with Stabilised
Phosphorus Ylide. To a stirred solution of Co(II)(SALEN)2 (7 mg, 0.02 mmol) in
CH2Cl2 (5 ml) was added 1,2-dioxine (1 mmol) at ambient temperature. The red
solution immediately turned a brown color and the consumption of 1,2-dioxine was
monitored using TLC. When complete, benzyl (triphenylphosphoranylidene)acetate
(492 mg, 1.2 mmol) was added and the mixture left to stir for 1-14 days until all
intermediate cis-γ-hydroxyenone had been consumed (TLC, 1H NMR). The solvent
was then removed in vacuo and products purified as specified.
(±±±±) Benzyl 2-[(1R,2S)-2-benzoylcyclopropyl]acetate (35c).50 Colourless oil; 1H
NMR (600 MHz) δ 1.03-1.09 (m, 1H), 1.55 (ddd, J = 8.9, 4.4, 4.4 Hz, 1H), 1.88-1.95
(m, 1H), 2.38 (dd, J = 15.8, 8.0 Hz, 1H), 2.59 (ddd, J = 8.3, 4.1, 4.1 Hz, 1H), 2.62 (dd,
J = 15.8, 6.2 Hz, 1H), 5.11 (d, J = 12.6 Hz, 1H), 5.13 (d, J = 12.6 Hz, 1H), 7.28-7.31
(m, 5H), 7.44-7.47 (m, 2H), 7.54-7.57 (m, 1H), 7.95-7.98 (m, 2H).
(±±±±) Benzyl 2-[2-(1R,2S)-benzoyl-3-methylcyclopropyl]acetate (35f).50 1H NMR
(600 MHz) δ 1.21 (d, J = 6.6 Hz, 3H), 1.87 (ddq, J = 10.8, 6.6, 4.4 Hz, 1H), 2.08
(dddd, J = 10.8, 7.8, 6.8, 4.4 Hz, 1H), 2.26 (dd, J = 4.4, 4.4 Hz, 1H), 2.52 (dd, J =
16.1, 7.8 Hz, 1H), 2.61 (dd, J = 16.1, 6.8 Hz, 1H), 5.12 (m, 2H), 7.29-7.30 (m, 5H).
(±±±±) Benzyl 2-[(1R,2S)-2-octanoylcyclopropyl]acetate (35g). Colourless oil purified
by successive flash chromatography; Rf 0.60 (70:30 hexane/ethyl acetate); IR (neat)
2928, 2851, 1731, 1698, 1455, 1259, 1167 cm-1; 1H NMR (300 MHz) δ 0.80 (ddd, J =
8.1, 6.3, 4.2 Hz, 1H), 0.87 (t, J = 6.6 Hz, 3H), 1.26-1.32 (m, 10H), 1.53-1.58 (m, 1H),
1.63-1.73 (m, 1H), 1.81 (ddd, J = 8.1, 4.5, 4.2 Hz, 1H), 2.25 (dd, J = 15.9, 7.8 Hz,
1H), 2.39-2.55 (m, 3H), 5.11-5.14 (m, 2H), 7.32-7.38 (m, 5H); 13C NMR (75 MHz) δ
14.0, 16.6, 20.1, 22.5, 23.8, 27.4, 29.0, 29.1, 31.6, 37.9, 43.6, 66.4, 128.1, 128.2,
110
128.5, 135.8, 171.6, 209.5; MS (EI) m/z (%): 316 (M+, 5), 232 (80), 91 (100); HRMS
calcd for (M+Na, ESI) C20H28O3Na: 339.1936; found: 339.1936.
(±±±±) Benzyl 2-[(1R,2S)-2-acetylcyclopropyl]acetate (35i).63,94 Isolated as a mixture
with (42i) as a colourless oil; 1H NMR (600 MHz) δ 0.82 (ddd, J = 9.0, 4.5, 4.5 Hz,
1H), 1.31 (ddd, J = 9.0, 4.5, 4.5 Hz, 1H), 1.66-1.71 (m, 1H), 1.82 (ddd, J = 8.4, 4.2,
4.2 Hz, 1H), 2.18 (s, 3H), 2.26 (dd, J = 16.2, 7.8 Hz, 1H), 2.49 (dd, J = 16.2, 6.6 Hz,
1H), 5.08 (d, J = 12.4 Hz, 1), 5.11 (d, J = 12.4 Hz, 1H), 7.30-7.38 (m, 5H).
(±±±±) Benzyl 2-[(1R,2S)-2-cyclohexylcarbonyl)cyclopropyl]acetate (35j). Colourless
oil purified by flash chromatography; Rf 0.50 (80:20 hexane/ethyl acetate); IR (neat)
2930, 2854, 1737, 1691, 1449, 1403, 1169, 698 cm-1; 1H NMR (600 MHz) δ 0.78
(ddd, J = 8.4, 5.6, 4.2, 1H), 1.15-1.35 (m, 6H), 1.62-1.68 (m, 2H), 1.74-1.77 (m, 2H),
1.84-1.89 (m, 3H), 2.24 (dd, J = 15.6, 8.4, 1H), 2.42 (dddd, J = 10.8, 10.8, 3.6, 3.6
Hz, 1H), 2.50 (dd, J = 15.6, 6.0 Hz, 1H); 5.10-5.14 (m, 2H), 7.31-7.37 (m, 5H); 13C
NMR (50 MHz) δ 16.6, 20.1, 25.5, 25.6, 25.8, 25.9, 28.2, 28.2, 37.9, 51.3, 66.3,
128.1, 128.2, 128.5, 135.7, 171.5, 211.9; MS (EI) m/z (%): 300 (M+, 20), 259 (15), 91
(100); HRMS calcd for (M+Na, ESI) C19H24O3Na: 323.1623 ; found: 323.1619.
(±±±±) Benzyl 2-[(1S,2R,3R)-2-acetyl-3-phenylcyclopropyl]acetate (69). Colourless oil
purified by flash chromatography; Rf 0.25 (CH2Cl2); IR (neat) 3031, 1737, 1698,
1603, 1498, 1421, 1356, 1164, 699 cm-1; 1H NMR (300 MHz) δ 2.03-2.14 (m, 2H),
2.26-2.36 (m, 2H), 2.28 (s, 3H), 2.91 (dd, J = 8.1, 4.8 Hz, 1H), 5.06 (d, J = 12.4 Hz,
1H), 5.08 (d, J = 12.4 Hz, 1H), 7.13-7.38 (m, 10H); 13C NMR (75 MHz) δ 26.4, 30.6,
32.5, 32.8, 33.1, 66.3, 126.9, 128.2, 128.2, 128.3, 128.5, 128.7, 135.4, 135.7, 171.7,
206.3; MS (EI) m/z (%): 308 (M+, 5), 290 (10), 217 (10), 91 (100); Anal calcd for
C20H20O3: C, 77.90; H, 6.54; Found: C, 77.97; H, 6.64.
(±±±±) Benzyl (2E,4Z)-6-hydroxy-6-phenyl-2,4-hexadienoate (70c). Colourless oil
purified by successive flash chromatography; Rf 0.26 (70:30 hexane/ethyl acetate); IR
(neat) 3418, 3031, 1713, 1638, 1269, 1168, 1026, 697 cm-1; 1H NMR (200 MHz) δ
2.33 (br d, J = 3.0 Hz, 1H), 5.19 (s, 2H), 5.75 (br dd, J = 9.0, 3.0 Hz, 1H), 5.91-6.03
(m, 2H), 6.25 (dd, J = 10.8, 11.6 Hz, 1H), 7.33-7.44 (m, 10H), 7.87 (ddd, J = 15.4,
11.6, 1.0 Hz, 1H); 13C NMR (50 MHz) δ 66.3, 69.9, 123.4, 125.9, 126.8, 127.8, 128.2,
111
128.5, 128.7, 135.9, 139.0, 140.8, 142.2, 166.5 (1 masked aromatic); MS (EI) m/z
(%): 294 (10), 278 (50), 263 (30), 105 (30), 91 (100); HRMS calcd for C19H18O3 :
294.1255; found: 294.1247.
(±±±±) Benzyl (2E,4Z)-6-hydroxy-5-methyl-6-phenyl-2,4-hexadienoate (70d).
Colourless solid purified by chromatography then recrystallisation (CH2Cl2/hexane);
mp 110°C (softens at 92°C); Rf 0.22 (70:30 hexane/ethyl acetate); IR (nujol) 3414,
1678, 1626, 1603, 1292, 1157, 1044 cm-1; 1H NMR (300 MHz) δ 1.76 (s, 3H), 2.10
(br d, J = 3.0 Hz, 1H), 5.17-5.23 (m, 2H), 5.95 (d, J = 15.0 Hz, 1H), 5.99 (d, J = 3.0
Hz, 1H), 6.14 (dpent, J = 11.7, 0.6 Hz, 1H), 7.27-7.40 (m, 10H), 7.91 (dd, J = 15.0,
11.7 Hz, 1H); 13C NMR (75 MHz) δ 18.5, 66.2, 71.1, 121.1, 125.5, 125.6, 127.4,
128.1, 128.2, 128.4, 128.5, 136.1, 139.4, 141.2, 149.0, 167.0; MS (EI) m/z (%): 308
(M+, 4), 291 (10), 201 (20), 91 (100); Anal calcd for C20H20O3: C, 77.90; H, 6.54;
Found: C, 77.71; H, 6.38.
(±±±±) Benzyl (2E,4Z)-6-hydroxy-2,4-tridecadienoate (70g). Colourless oil purified by
successive flash chromatography. Rf 0.30 (70:30 hexane/ethyl acetate); IR (neat)
3412, 2928, 1711, 1640, 1607, 1455, 1269, 1168, 910, 732 cm-1; 1H NMR (300 MHz)
δ 0.87 (t, J = 6.6 Hz, 3H), 1.23-1.70 (m, 12H), 1.73 (br s, 1H), 4.63-4.71 (m, 1H),
5.16-5.24 (m, 2H), 5.78 (ddd, J = 11.7, 9.6, 1.2 Hz, 1H), 5.96 (d, J = 15.3 Hz, 1H),
6.15 (ddd, J = 11.7, 11.7, 1.2 Hz, 1H), 7.29-7.39 (m, 5H), 7.63 (ddd, J = 15.3, 11.7,
1.2 Hz, 1H); 13C NMR (75 MHz) δ 14.0, 25.1, 25.5, 29.1, 29.4, 31.7, 37.3, 66.2, 67.9,
122.7, 127.0, 128.1, 128.2, 128.5, 135.9, 139.2, 142.3, 166.6; MS (EI) m/z (%): 316
(M+, 5), 225 (30), 91 (100); HRMS calcd for C20H28O3: 316.2038; found: 316.2027.
(±±±±) Benzyl (2E,4Z)-6-hydroxy-2,4-heptadienoate (70i). Colourless oil purified by
flash chromatography; Rf 0.29 (70:30 hexane/ethyl acetate); IR (neat) 3413, 2972,
1713, 1638, 1608, 1455, 1377, 1269, 1135, 1104 cm-1; 1H NMR (300 MHz) δ 1.30 (d,
J = 6.3 Hz, 3H); 1.73 (br s, 1H), 4.84-4.93 (m, 1H), 4.93-5.19 (m, 2H), 5.82 (dddd, J
= 10.8, 9.9, 0.9, 0.9 Hz, 1H), 5.96 (ddd, J = 15.0, 0.9, 0.9 Hz, 1H), 6.09 (dddd, J =
11.7, 10.8, 0.9, 0.9 Hz, 1H), 7.28-7.39 (m, 5H), 7.63 (ddd, J = 15.0, 11.7, 0.9, 1H); 13C NMR (50 MHz) δ 23.4, 64.0, 66.2, 122.7, 126.1, 128.2, 128.5, 135.9, 139.0,
143.2, 166.6 (1 masked aromatic); MS (EI) m/z (%): 232 (M+, 5), 214 (20), 201 (40),
91 (100); HRMS calcd for C14H17O3 (MH+): 233.1177, found: 233.1182.
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(±±±±) Benzyl (2E,4Z)-6-cyclohexyl-6-hydroxy-2,4-hexadienoate (70j). Colourless
solid purified by chromatography then recrystallisation (CH2Cl2/hexane); mp 54-56
°C; Rf 0.31 (80:20 hexane/ethyl acetate); IR (nujol) 3509, 1692, 1633, 1607, 1307,
1275, 733 cm-1; 1H NMR (300 MHz) δ 0.85-1.26 (m, 5H), 1.38-1.48 (m, 1H), 1.57-
1.69 (m, 5H), 1.93 (d, J = 12.6 Hz, 1H), 4.40 (dd, J = 9.5, 7.2 Hz, 1H), 5.16-5.25 (m,
2H), 5.80 (dd, J = 11.4, 9.5 Hz, 1H), 5.97 (d, 15.0 Hz, 1H), 6.22 (dd, J = 11.4, 11.4
Hz, 1H), 7.32-7.39 (m, 5H), 7.62 (ddd, J = 15.0, 11.4, 0.6 Hz, 1H); 13C NMR (50
MHz) δ 25.9, 26.0, 26.3, 28.5, 28.5, 43.9, 66.2, 72.1, 122.7, 127.8, 128.1, 128.5,
136.0, 139.4, 141.2, 166.6 (1 masked aromatic); MS (EI) m/z (%): 300 (M+, 10), 283
(40), 91 (100); Anal. calcd for C19H24O3: C, 75.97; H, 8.05; Found: C, 75.83; H, 8.11.
(±±±±) [(2R,3S)-5-Oxo-3-(2-oxopropyl)tetrahydro-2-furanyl]methyl acetate (72). To a
stirred solution of Co(II)(SALEN)2 (12 mg, .036 mmol) was added 1,2-dioxine (1j)
(500 mg, 3.84 mmol). After 30 minutes benzyl ylide (34a) (1.95g, 4.7 mmol) was
added and the reaction mixture allowed to stir for 14 days. The mixture was then
concentrated in vacuo and acetic anhydride (2 ml) and pyridine (2 ml) were added.
The reaction mixture was stirred for another 16 hours and then concentrated in vacuo
(.01 mmHg) at ambient temperature. From the complex mixture of compounds was
isolated the major component as a colourless oil (321 mg, 39%); Rf 0.60 (ethyl
acetate); IR (neat) 2960, 1782, 1744, 1714, 1422, 1366, 1237, 1168, 1049, 735 cm-1; 1H NMR (600 MHz) δ 2.09 (s, 3H), 2.19 (s, 3H), 2.30 (dd, J = 17.4, 9.6 Hz, 1H), 2.68
(dd, J = 17.4, 8.4 Hz, 1H), 2.68-2.77 (m, 2H), 3.15 (m, 1H), 4.06 (dd, J = 12.6, 4.2
Hz, 1H), 4.32 (dd, 12.6, 3.6 Hz, 1H), 4.87 (ddd, J = 7.2, 4.2, 3.6 Hz, 1H); 13C NMR
(150 MHz) δ 20.7, 29.8, 32.6, 33.9, 42.8, 62.9, 78.3, 170.0, 175.3, 205.7; MS (EI) m/z
(%): 215 (MH+, 10), 154 (50), 43 (100); HRMS calcd for (MH+) C10H15O5: 215.0919,
found: 215.0919.
Cyclisation of Dienoate (70a) by Intramolecular Michael Addition. To a stirred
solution of dienoate (70a) (159 mg, 0.54 mmol) in THF cooled to 0°C was added
potassium tert-butoxide (12 mg, 0.1 mmol). A colour change from colourless to
brown was observed and the solution was allowed to stir for 10 minutes. After this
time, saturated citric acid (10 ml) was added and the solution extracted with ether
(3×10 ml) the ether extracts were washed with NaHCO3 (10 ml), dried and
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concentrated in vacuo. The residue was purified by flash chromatography (90:10
hexane/ethyl acetate) to give the two dihydrofurans (80) (51 mg, 32%) and (81) (56
mg, 35%).
(±±±±) Benzyl 2-[(2S,5S)-5-phenyl-2,5-dihydro-2-furanyl]acetate (80). A slightly
unstable oil which underwent decomposition when stored at ambient temperature for
1 week; IR (neat) 3064, 3032, 2876, 1731, 1603, 1494, 1455, 1257, 1162, 1061, 735
cm-1; 1H NMR (600 MHz) δ 2.66 (dd, J = 15.0, 6.0 Hz, 1H), 2.77 (dd, J = 15.0, 7.2
Hz, 1H), 5.14 (d, J = 12.6 Hz, 1H), 5.17 (d, J = 12.6 Hz, 1H), 5.45 (dddd, J = 7.2, 6.0,
3.6, 1.8, 2.4 Hz, 1H), 5.79 (ddd, J = 3.6, 1.8, 1.8 Hz, 1H), 5.91 (ddd, J = 6.6, 1.8, 1.8
Hz, 1H), 5.99 (ddd, J = 6.6, 2.4, 1.8 Hz, 1H), 7.25-7.38 (m, 10H); 13C NMR (150
MHz) δ 41.1, 66.3, 82.7, 87.6, 126.3, 127.8, 128.2, 128.2, 128.4, 128.5, 128.9, 131.2,
135.8, 141.3, 170.6; MS (EI) m/z (%): 294 (M+, 2), 293 (10), 203 (40), 157 (35), 91
(100); HRMS calcd for (M+Na+, ESI) C19H18O3Na1: 317.1153, found: 317.1154.
(±±±±) Benzyl 2-[(2S,5R)-5-phenyl-2,5-dihydro-2-furanyl]acetate (81). A slightly
unstable oil which underwent decomposition when stored at ambient temperature for
1 week; IR (neat) 3064, 3032, 2861, 1731, 1494, 1455, 1259, 1161, 1060, 739, 698
cm-1; 1H NMR (600 MHz) δ 2.69 (dd, J = 15.0, 6.0 Hz, 1H), 2.80 (dd, J = 15.0, 7.2
Hz, 1H), 5.12 (d, J = 12.6 Hz, 1H), 5.17 (d, J = 12.6 Hz, 1H), 5.33 (dddd, J = 7.2, 6.0,
2.4, 1.8, 1.8 Hz, 1H), 5.79 (ddd, J = 1.8, 1.8, 1.8 Hz, 1H), 5.92 (ddd, J = 6.0, 1.8, 1.8
Hz, 1H), 5.98 (ddd, J = 6.0, 2.4, 1.8 Hz, 1H), 7.25-7.36 (m, 10H); 13C NMR (150
MHz) δ 41.9, 66.4, 82.5, 88.0, 126.5, 128.2, 128.2, 128.4, 128.4, 129.2, 131.4, 135.7,
141.4, 170.5 (1 masked aromatic); MS (EI) m/z (%): 295 (MH+, 10), 293 (10), 203
(100), 157 (30), 91 (40); HRMS calcd for (M-H2, EI) C19H16O3: 292.1099, found:
292.1100.
8.4 Compounds Described in Chapter 4.
The Synthesis of Stabilised Phosphorus Ylides (34d) and (34e).
Diphenylmethyl 2-bromoacetate (84a).161 Benzophenone hydrazone (5.0 g, 25.2
mmol) and yellow mercuric oxide (5.6 g, 25.9 mmol) were added to hexane (25 ml)
and the flask sealed with a septum. The septum then secured with copper wire and the
114
mixture stirred for 6 hours. The purple solution was filtered and the precipitate
washed with a small portion of hexane. The filtrate was added dropwise to
bromoacetic acid (2.66 g, 19 mmol) in acetone (10 ml) until the solution remained
purple. One drop of glacial acetic acid was added to discharge the colour and then the
volatiles removed in vacuo to give the title compound as a colourless oil (5.80 g,
100%); 1H NMR (200 MHz) δ 3.92 (s, 2H), 6.91 (s, 1H), 7.31-7.37 (m, 5H).
1-Adamantyl 2-bromoacetate (84b).162 A solution of bromoacetic acid (6.35 g, 46
mmol), 1-adamantanol (3.5 g, 23 mmol) and p-toluenesulfonic acid (150 mg) were
refluxed together in benzene (60 ml) for 16 hours and water removed using a Dean-
Stark trap. After cooling the solution was washed with sodium bicarbonate (3×40 ml)
and aqueous washings extracted with ether (30 ml). The combined organic extracts
were dried (Na2SO4) and concentrated in vacuo to afford the title compound as a
colourless oil (5.64 g, 90%); IR (Neat) 2913, 2857, 1732, 1456, 1278, 1169, 1103,
1053 cm-1; 1H NMR (300 MHz) δ 3.75 (2H, s), 2.18 (3H, br s), 2.12 (6H, br s), 1.66
(6H, br s); 13C NMR (75 MHz) δ 27.8, 30.8, 36.0, 41.0, 82.9, 165.8; MS (EI) m/z (%):
273 (M+, 10), 194, 135.
Diphenylmethyl 2-(1,1,1-triphenyl-λ5-phosphanylidene)acetate (34d).99 A solution
of diphenylmethyl bromoacetate (5.64 g, 20 mmol), was added to triphenylphosphine
(6.02 g, 23 mmol) in dry toluene (50 ml) and the mixture heated to 80oC. After 16
hours the precipitated white solid was collected by filtration and washed successively
with hexane (50 ml) then ether (50 ml) and dried under an IR lamp. The salt was then
dissolved in a minimal amount of 1:1 methanol/water and a solution of 1N NaOH
added dropwise with vigorous stirring until no more ylide precipitated. The
precipitate was collected, washed with water (50 ml) and recrystallised from hexane
to a colourless solid (6.0 g, 62%); IR (nujol) 1643, 1592, 1231, 1104, 1021 cm-1; 1H
NMR (300 MHz) δ 2.80-3.20 (br s, 1H)), 6.87 (s, 1H), 7.04-7.24 (m, 8H), 7.34-7.44
(m, 7H), 7.48-7.64 (m, 10H).
1-Adamantyl 2-(1,1,1-triphenyl-λ5-phosphanylidene) acetate (34e). A solution of
1-adamantyl bromoacetate (5.64 g, 20 mmol), was added to triphenylphosphine (6.02
g, 23 mmol) in dry toluene (50 ml) and the mixture heated to 80oC. After 16 hours the
precipitated white solid was collected by filtration and washed successively with
115
hexane (50 ml) then ether (50 ml) and dried under an IR lamp. The salt was then
dissolved in a minimal amount of 1:1 methanol/water and a solution of 1N NaOH
added dropwise with vigorous stirring until no more ylide precipitated. The
precipitate was collected, washed with water (50 ml) and recrystallised from hexane
to afford cream crystals (6.4 g, 69%); mp 145-148 oC; IR (nujol) 2916, 1629, 1280,
1211, 1101, 1068 cm-1; 1H NMR (300 MHz) δ 1.4-2.2 (m, 15H), 2.4-3.0 (br s, 1H),
7.36-7.68 (m, 15H); 13C NMR (50 MHz) δ 30.7, 32.4, 36.4, 41.0, 128.3 (d, J = 89
Hz), 128.4 (d, J = 12 Hz), 131.5 (d, J = 3.0 Hz), 132.8 (d, J = 9.8 Hz), 170.8; 31P
NMR δ 17.4; MS (EI) m/z (%): 454 (M+), 277 (100); Anal. Calcd. for C30H31O2P1: C,
79.27; H, 6.87; Found: C, 78.82; H, 6.78.
General Procedure for the Reaction of Bulky Ylides (34d) and (34e) with 1,2-
Dioxines (1b), (1c) and (1k).
(±±±±) Diphenylmethyl [(1S,2R,3R)-2-(2-benzoyl-3-phenylcyclopropyl)]acetate (86b).
To a stirred solution of 1,2-dioxine (1b) (200 mg, 0.84 mmol) in CH2Cl2 (9 ml,
0.10M) at 0°C was added ylide (34d) (540 mg, 1.26 mmol). The reaction progress
was followed using TLC and after complete consumption of starting material was
observed (ca. 10 days) the mixture was concentrated in vacuo. Purification by flash
chromatography (90:10 hexane/ethyl acetate) followed by recrystallisation
(CH2Cl2/heptane) afforded (86b) (250 mg, 67%); mp 117-118 °C Rf 0.20 (9:1
hexane:ethyl acetate); IR (nujol): 1724, 1657, 1462, 1377, 1250, 703 cm-1; 1H NMR
(600 MHz) δ 2.23 (dd, J = 16.2, 7.8 Hz, 1H), 2.41 (dddd, J = 9.6, 7.8, 6.6, 4.8, 1H),
2.50 (dd, J = 16.2, 6.6 Hz, 1H), 3.05 (dd, J = 4.8, 4.8 Hz, 1H), 3.10 (dd, J = 9.6, 4.8
Hz, 1H), 6.81 (s, 1H), 7.14-7.28 (m, 15H), 7.43-7.46 (m, 2H), 7.54-7.57 (m, 1H),
7.98-8.00 (m, 2H); 13C NMR (75 MHz) δ 20.6, 27.7, 32.8, 41.5, 126.5, 126.8, 127.3,
127.7, 127.7, 128.0, 128.4, 129.1, 130.8, 132.9, 135.5, 136.3, 139.6, 139.9, 169.2,
197.7; MS (EI) m/z (%): 446 (M+, 75), 167 (95), 105 (100); Anal. calcd for C31H26O3:
C, 83.38; H, 5.86; Found: C, 83.56; H, 5.88.
(±±±±) Diphenylmethyl (1S,2R,3R)-2-(2-oxo-2-phenylethyl)-3-phenylcyclopropane-1-
carboxylate (90b). Recrystallised from hot hexane to give colourless needles; mp
136-138oC; Rf 0.67 (80:20 hexane/ethyl acetate); IR (nujol): 1712, 1691, 1154, 1072,
1031, 954, 727, 699 cm-1; 1H NMR (600 MHz) δ 2.16 (dd, J = 9.0, 5.4 Hz, 1H), 2.51-
116
2.58 (m, 2H), 2.93 (dd, J = 16.8, 7.8 Hz, 1H), 3.42 (dd, J = 16.8, 5.4 Hz, 1H), 6.67 (s,
1H), 7.05-7.28 (m, 15H), 7.46-7.48 (m, 1H), 7.56-7.59 (m, 2H), 7.95-7.96 (m, 2H); 13C NMR (75 MHz) δ 20.9, 28.0, 33.1, 41.8, 126.8, 127.1, 127.1, 127.6, 127.6, 128.0,
128.0, 128.0, 128.2, 128.7, 129.4, 133.2, 135.8, 136.6, 139.9, 140.2, 169.5, 198.0; MS
(EI) m/z (%): 445 (M+, 4), 339 (10), 166 (100); Anal. calcd for C31H26O3: C, 83.38; H,
5.86; Found: C, 83.36; H, 5.61.
To a stirred solution of 1,2-dioxine (1b) (1.00 g, 4.2 mmol) in CH2Cl2 (25 ml, 0.16 M)
at 25oC was added adamantyl ester ylide (34e) (2.5 g, 5.5 mmol). After complete
consumption of starting materials had occurred (TLC), workup as per the general
procedure afforded (87b), (91b) and (94b).
(±±±±) 1-Adamantyl [(1S,2R,3R)-2-(2-oxo-2-phenylethyl)-3-
phenylcyclopropyl]acetate (87b). Purified by flash chromatography to give a
colourless oil (452 mg, 25%); Rf 0.13 (benzene); IR (nujol): 2924, 1733, 1673, 1168,
1056 cm-1; 1H NMR (300 MHz) δ 1.58 (br s, 6H), 1.97 (br s, 6H), 2.01-2.10 (m, 4H),
2.3-2.23 (m, 2H), 3.05 (t, J = 4.5 Hz, 1H), 3.14 (dd, J = 5.1, 8.7 Hz, 1H), 7.20-7.61
(m, 8H), 8.05-8.07 (m, 2H); 13C NMR (75 MHz) δ 27.9, 29.7, 30.7, 33.5, 34.6, 36.0,
41.1, 80.7, 126.8, 128.1, 128.3, 128.5, 128.7, 128.9, 132.8, 136.1, 137.8, 170.9, 198.5;
MS (EI) m/z (%): 414 (M+, 15), 279 (80), 135 (100); HRMS Calcd for (M+) C28H30O3:
414.2194; found: 414.2185.
(±±±±) 1-Adamantyl (1S,2R,3R)-2-(2-oxo-2-phenylethyl)-3-phenylcyclopropane-1-
carboxylate (91b). Recrystallised from diethylether/pentane by vapour diffusion to
give colourless needles (829 mg, 48%); mp 102-104oC; Rf 0.67 (20%EtOAc/hexane);
IR (nujol): 2923, 1695, 1690, 1593, 1273, 1212, 1067 cm-1; 1H NMR (600 MHz) δ
1.53 (m, 6H); 1.74 (m, 6H), 1.89 (dd, J = 5.4, 9.0 Hz, 1H), 2.01 (br s, 3H), 2.40-2.45
(m, 2H), 2.86 (dd, J = 7.8, 17.4 Hz, 1H), 3.44 (dd, J = 4.2, 17.4 Hz, 1H), 7.17-7.20
(m, 1H), 7.25-7.27 (m, 2H), 7.35-7.36 (m, 2H), 7.46-7.49 (m, 2H), 7.56-7.59 (m, 1H),
7.96-7.97 (m, 2H), 13C NMR (75 MHz) δ 20.0, 28.9, 30.7, 32.4, 36.1, 41.0, 41.8, 80.4,
126.5, 127.8, 128.0, 128.6, 129.6, 133.1, 136.5, 136.7, 169.2, 198.3; MS (EI) m/z (%):
414 (M+, 10), 135 (100); Anal. Calcd for C28H30O3: C, 81.12; H, 7.29; Found: C,
81.26; H, 7.31.
117
(±±±±) 1-Adamantyl (1R,2R,3R)-2-(2-oxo-2-phenylethyl)-3-phenylcyclopropane-1-
carboxylate (94b). Purified by flash chromatography to give a colourless oil (101 mg,
6%); Rf 0.23 (benzene); IR (neat): 2851, 1714, 1695, 1607, 1338, 1179, 1119, 1105
cm-1; 1H NMR (600 MHz) δ 1.62 (m, 6H), 2.07 (m, 6H), 2.03-2.08 (m, 1H), 2.11 (br
s, 3H), 2.15 (dd, J = 5.4, 9.0 Hz, 1H), 2.43 (dd, J = 5.4, 6.0 Hz, 1H), 3.45 (dd, J = 7.2,
18 Hz, 1H), 3.52 (dd, J = 6.0, 18 Hz, 1H), 7.3-7.15 (m, 5H), 7.46 (m, 2H), 7.55 (m,
1H), 7.97 (m, 2H); 13C NMR (75 MHz) δ 25.0, 29.2, 30.7, 30.9, 36.1, 36.2, 41.2, 80.9,
125.6, 126.3, 128.0, 128.3, 128.4, 128.5, 133.0, 140.0, 170.9, 199.0; MS (EI) m/z (%):
414 (M+, 3), 279 (50), 262 (45), 135 (100); HRMS Calcd for (M+) C28H30O3:
414.2194; Found: 414.2182.
A stirred solution of 1,2-dioxine (1b) (200 mg, 0.84 mmol) and adamantyl ester ylide
(34e) (572 mg, 1.26 mmol) in toluene (5 ml) was heated to 100 °C for 3 days. The
cooled solution was concentrated in vacuo and (87b) (180 mg, 51%) isolated by flash
chromatography.
A solution of 1,2-dioxine (1c) (500 mg, 3.08 mmol) and adamantyl ylide (34e) (1.36g,
3.00 mmol) was stirred for 14 days then evaporated. Purification by flash
chromatography afforded (91c) (319 mg, 38%) and (94c) (39 mg, 5%) based on the
recovery of starting dioxine (1c) (93 mg).
(±±±±) 1-Adamantyl (1R,2S)-2-(2-oxo-2-phenylethyl)cyclopropyl)acetate (87c).
Purified by flash chromatography to give a colourless oil; Rf 0.50 (2.5%
Et2O/Benzene); IR (neat) 1727, 1668, 1598, 1450, 1402, 1223, 1180, 1056 cm-1; 1H
NMR (600 MHz) δ 0.98 (ddd, J = 4.0, 6.4, 8.0 Hz, 1H), 1.56 (ddd, J = 4.0, 4.8, 8.8
Hz, 1H), 1.61 (m, 6H), 1.83 (m, 1H), 2.03 (br s, 6H), 2.14 (brs, 3H), 2.22 (dd, J = 7.8,
15.3 Hz, 1H), 2.46 (dd, J = 6.4, 15.3 Hz, 1H), 2.57 (ddd, J = 4.0, 4.8, 8.0 Hz, 1H),
7.44-7.47 (m, 2H), 7.53-7.56 (m, 1H), 7.98-8.00 (m, 2H); 13C NMR (50 MHz) δ 17.5,
22.2, 24.4, 30.8, 36.1, 39.6, 41.3, 80.8, 128.0, 128.4, 132.7, 137.9, 170.8, 199.3; MS
(LSIMS) m/z (%): 339 (MH+, 30), 135 (100); Anal. Calcd for C22H26O3: C, 78.07; H,
7.74; Found: C, 78.11; H, 7.86.
(±±±±) 1-Adamantyl (1R,2S)-2-(2-oxo-2-phenylethyl)cyclopropane-1-carboxylate
(91c). Recrystallised from CH2Cl2/hexane to give white crystals; mp 101-102 oC; Rf
118
0.37 (1:40 diethyl ether/benzene); IR (nujol) 1714, 1685, 1268, 1085, 1058 cm-1; 1H
NMR (600 MHz) δ 0.76 (ddd, J = 8.6, 6.3, 4.5 Hz, 1H) 1.24 (ddd, J = 8.6, 4.6, 4.3 Hz,
1H), 1.42 (ddd, J = 4.3, 4.3, 8.7 Hz, 1H), 1.65 (br s, 6H), 1.76 (m, 1H), 2.11 (brs, 6H),
2.16 (brs, 3H), 2.80 (dd, J = 7.2, 16.8 Hz, 1H), 3.19 (dd, J = 6, 16.8 Hz, 1H), 7.44-
7.46 (m, 2H), 7.54-7.56 (m, 1H), 7.90-7.92 (m, 2H); 13C NMR (75 MHz) δ 14.7, 17.2,
21.1, 30.7, 36.1, 41.3, 42.0, 80.4, 128.0, 128.6, 133.1, 136.5, 172.6, 198.4; MS (EI)
m/z (%): 338 (M+, 25), 203 (45), 135 (100); Anal. Calcd for C22H26O3: C, 78.07; H,
7.74; Found: C, 78.27; H, 7.83.
(±±±±) 1-Adamantyl (1R,2R)-2-(2-oxo-2-phenylethyl)cyclopropane-1-carboxylate
(94c). Purified by flash chromatography to give a colourless oil; Rf 0.47 (2.5%
Et2O/Benzene); IR (neat) 1714, 1685, 1268, 1085, 1058; 1H NMR (600 MHz) δ 0.91
(ddd, J = 4.6, 5.2, 7.0 Hz, 1H), 1.11 (ddd, J = 4.6, 8.1, 8.2Hz, 1H), 1.61 (m, 6H), 1.65
(m, 1H), 1.66 (ddd, J = 5.2, 8.1, 8.8 Hz, 1H), 2.05 (m, 6H), 2.10 (br s, 3H), 3.26 (dd, J
= 7.5, 18.1 Hz, 1H), 3.33 (dd, J = 6.5, 18.1 Hz, 1H), 7.43-7.45 (m, 2H), 7.52-7.55 (m,
1H), 7.93-7.95 (m, 2H); 13C NMR (150 MHz) δ 13.0, 15.8, 18.7, 30.7, 36.1, 36.5,
41.3, 80.5, 128.0, 128.5, 132.9, 137.0, 172.2, 199.6; MS (LSIMS) m/z (%): 339 (MH+,
20), 135 (100); HRMS calcd for C22H27O3 (MH+): 339.1960; found: 339.1952.
To a stirred solution of 3,6-dipropyl-1,2-dioxine (1k) (500 mg, 2.94 mmol) dissolved
in CH2Cl2 (15 ml) was added Co(II)(SALEN)2 (5 mg). After 15 minutes, benzyl ylide
(34a) (1.45 g, 3.52 mmol) was added and the reaction mixture allowed to stir for 3
days at room temperature. After this time, the volatiles were removed in vacuo
leaving a brown residue. Purification by successive flash chromatography (90:10
hexane/ethyl acetate) afforded the two cyclopropanes (35k) (209 mg, 24%)and (42k)
(159 mg, 16%).
Benzyl 2-[(1R,2S,3S)-2-(1-oxobutyl)-3-propylcyclopropyl]acetate (35k).
Colourless oil; Rf 0.38 (90:10 hexane/ethyl acetate); IR (neat) 2961, 2932, 2873,
1738, 1693, 1455, 1166 cm-1; 1H NMR (600 MHz) δ 0.89 (t, J = 7.2 Hz, 3H), 0.89 (t,
J = 7.2 Hz, 3H), 1.23-1.28 (m, 1H), 1.35-1.43 (m, 3H), 1.53 (dd, J = 4.5, 4.5 Hz, 1H),
1.54-1.61 (m, 3H), 1.84 (dddd, J = 4.5, 6.6, 8.4, 9.0 Hz, 1H), 2.36 (dd, J = 8.4, 16.2
Hz, 1H), 2.37-2.46 (m, 2H), 2.52 (dd, J = 6.6, 16.2 Hz, 1H), 5.12 (m, 2H), 7.31-7.36
(m, 5H); 13C NMR (150 MHz) δ 13.6, 13.7, 17.4, 22.4, 25.0, 29.1, 29.6, 32.8, 34.6,
119
45.5, 66.3, 128.1, 128.2, 128.5, 135.7, 171.9, 209.4; MS (EI) m/z (%): 303 (MH+, 2),
211 (10), 91 (100); Anal. Calcd for C19H26O3: C, 75.46; H, 8.66; Found: C, 75.57; H,
8.51.
Benzyl 2-[(1R,2R,3S)-2-(1-oxobutyl)-3-propylcyclopropyl]acetate (42k).
Colourless oil; Rf 0.45 (90:10 hexane/ethyl acetate); IR (neat) 2959, 2928, 2872,
1737, 1690, 1604, 1456, 1392, 1167 cm-1; 1H NMR (600 MHz) δ 0.87 (t, J = 7.2 Hz,
3H), 0.88 (t, J = 7.2 Hz, 3H), 1.19-1.31 (m, 2H), 1.48-1.58 (m, 5H), 1.75 (dddd, J =
8.4, 8.4, 8.4, 6.0 Hz, 1H), 2.09 (dd, J = 8.4, 8.4 Hz, 1H), 2.48 (t, J = 7.2 Hz, 2H), 2.78
(dd, J = 17.4, 6.0 Hz, 1H), 2.89 (dd, J = 17.4, 8.4 Hz, 1H), 5.08 (d, J = 12.0 Hz, 1H),
5.10 (d, J = 12.0 Hz, 1H), 7.30-7.36 (m, 5H); 13C NMR (150 MHz) δ 13.6, 13.8, 17.3,
22.5, 22.7, 23.7, 26.5, 27.4, 27.6, 47.5, 66.0, 128.0, 128.0, 128.4, 136.0, 173.1, 209.8;
MS (EI) m/z (%): 303 (15), 211 (15), 91 (100).
Reactions of 1,2-Dioxines in the Presence of Ionic Additives.
To a stirred solution of 1,2-dioxine (1b) (238 mg, 1 mmol) dissolved in CH2Cl2 (10
ml) was added lithium bromide (174 mg, 2.0 mmol) then ylide (34d) (583 mg, 1.2
mmol) and a catalytic amount of Co(II)(SALEN)2. The reaction was allowed to stir
for 7 days then concentrated in vacuo and the mixture purified by flash
chromatography to give (90b) (95 mg, 21%).
To a stirred solution of 1,2-dioxine (1c) (162 mg, 1.0 mmol) in CH2Cl2 (10 ml) was
added 1-adamantyl (triphenylphosphoranylidene)acetate (34e) (605 mg, 1.28 mmol)
and lithium bromide (89 mg, 1.0 mmol). After 4 days stirring at room temperature the
reaction mixture was concentrated in vacuo and products separated by flash
chromatography (hexane/ethyl acetate, 9:1) to give (91c) (199 mg, 58%) and (94c)
(24 mg, 7%).
(±±±±) 1-Benzyl (1R,2S)-2-(2-benzoylcyclopropyl)acetate (42c). To a stirred solution of
3-phenyl-3,6-dihydro-1,2-dioxine (1c) (162 mg, 1.0 mmol) in CH2Cl2 (5 ml) was
added benzyl ylide (34a) (492 mg, 1.2 mmol) and sodium bromide (103 mg, 1.0
mmol). The reaction mixture was stirred for 72 hours and then concentrated in vacuo.
The crude reaction mixture was examined by 1H NMR and then purified by
120
successive flash chromatography until separation was achieved. In addition to the
previously isolated primary cyclopropane (35c)50 was isolated the previously
unobserved cyclopropane (42c) (11 mg, 4%) as a colourless oil; Rf 0.52 (CH2Cl2); IR
(neat) 3061, 3031, 1727, 1668, 1171, 1000 cm-1; 1H NMR (600 MHz) δ 1.22 (ddd, J =
4.2, 7.8, 8.4 Hz, 1H), 1.38 (ddd, J = 4.2, 5.7, 7.2 Hz, 1H), 1.89 (m, 1H), 2.55 (dd, J =
8.4, 17.4 Hz, 1H), 2.71 (dd, J = 6.0, 17.4 Hz, 1H), 2.85 (ddd, J = 5.7, 7.8, 9.0 Hz, 1H),
4.95 (d, J = 12.3 Hz, 1H), 4.98 (d, J = 12.3 Hz, 1H), 7.18-7.58 (m, 8H), 7.97 (m, 2H); 13C NMR (150 MHz) δ 13.9, 20.4, 22.3, 31.6, 66.0, 128.0, 128.0, 128.1, 128.4, 128.7,
132.6, 135.9, 138.7, 172.5, 198.9; MS (EI) m/z (%): 295 (MH+, 5), 203 (20), 160 (50),
105 (100); HRMS calcd for (MH+) C19H19O3: 295.1334; found: 295.1344.
A solution of 3-phenyl-3,6-dihydro-1,2-dioxine (1c) (162 mg, 1.0 mmol), lithium
bromide (86 mg, 1.0 mmol) and benzyl ester ylide (34a) (492 mg, 1.2 mmol) in
CH2Cl2 (5 ml) were stirred for 72 hours. After completion, the reaction mixture was
concentrated in vacuo and the products separated by flash chromatography (90:10
hexane/ethyl acetate) before being further purified as specified.
(±±±±) Benzyl (1S,2R)-2-(2-oxo-2-phenylethyl)cyclopropane-1-carboxylate (92c).
Recrystallised from ether/pentane by vapour diffusion (117 mg, 40%); Rf 0.25; mp
82.5-83.5 °C; IR (nujol) 1724, 1683, 1267, 1025; 1H NMR (300 MHz) δ 0.86 (ddd, J
= 4.6, 8.2, 9.3, 1H), 1.37 (ddd, J = 4.5, 4.5, 9.0 Hz, 1H), 1.58 (ddd, J = 4.5, 4.5, 8.5
Hz, 1H), 1.89 (m, 1H), 2.89 (dd, J = 7.2, 16.8 Hz, 1H), 3.10 (dd, J = 6.6, 16.8 Hz,
1H), 5.12 (d, J = 12.3 Hz, 1H), 5.14 (d, J = 12.3 Hz, 1H), 7.30-7.60 (m, 8H), 7.90-
7.95 (m, 2H); 13C NMR (75 MHz) δ 15.1, 17.8, 20.0, 41.9, 66.3, 128.0, 128.1, 128.1,
128.5, 128.6, 133.2, 133.0, 136.5, 173.5, 198.0; MS (EI) m/z (%): 294 (M+, 5), 188
(10), 105 (100); Anal. Calcd for C19H18O3: C, 77.53; H, 6.16; Found: C, 77.68; H,
6.08.
(±±±±) Benzyl (1S,2S)-2-(2-oxo-2-phenylethyl)cyclopropane-1-carboxylate (95c).
Purified by successive flash chromatography (benzene) to give a colourless oil (9 mg,
3%); Rf 0.40; IR (neat) 3068, 2957, 1727, 1687, 1451, 1401, 1162 cm-1; 1H NMR (300
MHz) δ 1.03 (ddd, J = 4.9, 5.2, 7.2 Hz, 1H), 1.23 (ddd, J = 4.9, 8.1, 8.1 Hz, 1H), 1.77
(m, 1H), 1.95 (ddd, J = 5.2, 8.1, 8.4 Hz, 1H), 3.28 (dd, 20.0, 6.8 Hz, 1H), 3.34 (dd, J =
20.0, 7.0 Hz, 1H), 5.05 (d, J = 12.0 Hz, 1H) 5.12 (d, J = 12 Hz, 1H), 7.20-7.60 (m,
121
8H), 7.90-7.93 (m, 2H); 13C NMR (75 MHz) δ 13.7, 16.5, 17.7, 36.5, 66.3, 128.0,
128.0, 128.1, 128.4, 128.5, 132.9, 136.1, 136.8, 173.1, 199.2; MS (EI) m/z (%): 295
(MH+, 15), 188 (18), 105 (100), HRMS Calcd for (M+) C19H18O3: 294.1255; found:
294.1258.
A solution of 3,6-dipropyl-3,6-dihydro-1,2-dioxine (1k) (170 mg, 1.0 mmol), lithium
bromide (86 mg, 1.0 mmol) and benzyl ester ylide (34a) (492 mg, 1.2 mmol) in
CH2Cl2 (5 ml) were stirred for 72 hours. After completion, the reaction mixture was
concentrated in vacuo and the products (82k) and (83k) separated by flash
chromatography (90:10 hexane/ethyl acetate) before being further purified as
specified:
(±±±±) tert-Butyl (1S,2R,3R)-2-(2-oxopentyl)-3-propylcyclopropane-1-carboxylate
(82k). A colourless oil purified by successive flash chromatography; Rf 0.40 (90:10
hexane/ethyl acetate); IR (neat) 2962, 1716, 1367, 1155 cm-1; 1H NMR (600 MHz) δ
0.89 (t, J = 6.6 Hz, 3H), 0.91 (t, J = 7.2 Hz, 3H), 1.05 (m, 1H), 1.45-1.65 (m, 8H),
1.44 (s, 9H), 2.22 (dd, J = 16.2, 7.8 Hz, 1H), 2.41 (dd, J = 7.2, 7.2 Hz, 2H), 2.46 (dd,
J = 16.2, 6.6 Hz, 1H); 13C NMR (150 MHz) δ 13.7, 13.7, 17.0, 21.9, 22.6, 26.0, 28.1,
28.7, 28.7, 44.1, 46.4, 80.2, 171.3, 209.5; MS (EI) m/z (%): 268 (M+, 21), 211 (40),
196 (100); HRMS calcd for C19H28O3 (M+): calc, 269.2117; found: 269.2113.
(±±±±) tert-Butyl (1R,2R,3R)-2-(2-oxopentyl)-3-propylcyclopropane-1-carboxylate
(83k). Colourless oil; Rf 0.60 (9:1 hexane/ethyl acetate); IR (neat) 2961, 2934, 1716,
1457, 1366, 1154 cm-1; 1H NMR (300 MHz) δ 0.89 (t, J = 7.5 Hz, 3H), 0.90 (t, J = 7.2
Hz, 3H), 1.2-1.63 (m, 9H), 1.44 (s, 9H), 2.35 (t, J = 7.5 Hz, 2H), 2.66-2.82 (m, 2H); 13C NMR (150 MHz) δ 13.7, 13.7, 17.2, 21.9, 23.0, 27.2, 28.0, 28.1, 34.9, 40.3, 44.5,
80.1, 172.3, 210.3; MS (EI) m/z (%): 269 (MH+, 30), 213 (52), 195 (100); HRMS
calcd for C16H28O3: 269.2117; found: 269.2113.
Procedure for the Synthesis of γγγγ-Lactones from Dioxine and Ylide.
To a stirred solution of 3,6-dipropyl-3,6-dihydro-1,2-dioxine (1k) (500 mg, 2.94
mmol) dissolved in CH2Cl2 (15 ml, 0.2 M) was added Co(II)(SALEN)2 (24) (5 mg)
then lithium bromide (255 mg, 2.94 mmol) and water (65 mg. 3.6 mmol). tert-Butyl
122
ylide (34c) (1.32 g, 3.5 mmol) was added and the reaction stirred at -15°C for 14 days.
After this time the solution was allowed to warm to room temperature and the solvent
removed in vacuo. Purification by flash chromatography (80:20 hexane/ethyl acetate)
gave the cyclopropanes (82k) and (83k) (144 mg, 14%) isolated as a mixture of
diastereomers and two oils (96) (108 mg, 13%); Rf 0.26 and (97) (295 mg, 35%); Rf
0.19. The two oils were characterised as the corresponding lactones by dissolving the
oil (25 mg) in CDCl3 (0.7 ml) and adding trifluoroacetic acid (10 mg). Quantitative
conversion to the lactones was seen after 16 hours. The solutions were then filtered
through short silica columns to remove the trifluoroacetic acid and dried in vacuo to
give (98) and (99).
(±±±±) (4S,5S)-4-(2-Oxopentyl)-5-propyltetrahydro-2-furanone (98). Colourless oil;
IR (neat) 2962, 1777, 1713, 1459, 1379, 1174, 990 cm-1; 1H NMR (CDCl3, 600) δ
0.89 (t, J = 7.2 Hz, 3H), 0.92 (t, J = 7.2 Hz, 3H), 1.22-1.55 (m, 4H), 1.58 (sept, J = 7.2
Hz, 2H), 2.18 (dd, J = 17.4, 6.6 Hz, 1H), 2.37-2.39 (m, 2H), 2.47 (dd, J = 18.0, 7.8
Hz, 1H), 2.58 (dd, J = 18.0, 6.0 Hz, 1H), 2.70 (dd, J = 17.4, 7.8 Hz, 1H), 2.99 (ddddd,
J = 7.8, 7.8, 6.6, 6.0, 6.0 Hz, 1H), 4.58 (ddd, J = 3.0, 6.0, 9.6 Hz, 1H); 13C NMR (75)
δ 13.6, 13.7, 17.2, 19.1, 32.2, 33.7, 35.1, 41.4, 45.0, 82.8, 177.2, 208.8; MS (EI) m/z
(%) 212 (M+, 8), 169 (70), 71 (95), 43 (100); HRMS calcd for C12H20O3: 212.1412;
found: 212.1414.
(±±±±) (4R,5S)-4-(2-Oxopentyl)-5-propyltetrahydro-2-furanone (99). Colourless oil;
IR (neat): 2965, 1779, 1709, 1462, 1380, 1215, 1168 cm-1; 1H NMR (600, CDCl3) δ
0.92 (t, J = 7.2 Hz, 3H), 0.95 (t, J = 7.2 Hz, 3H), 1.40-1.66 (m, 6H), 2.17 (dd, J =
17.4, 6.0 Hz, 1H), 2.40 (t, J = 7.2 Hz, 2H), 2.53 (dd, J = 17.4, 7.8 Hz, 1H), 2.61
(ddddd, J = 9.0, 7.8, 6.6, 6.0, 5.4 Hz, 1H), 2.69 (dd, J = 17.4, 6.9 Hz, 1H), 2.86 (dd, J
= 18.0, 9.0 Hz, 1H), 4.19 (ddd, J = 7.8, 6.0, 4.8 Hz, 1H); 13C NMR (150, CDCl3) δ
13.5, 13.7, 17.1, 18.7, 34.9, 35.7, 36.4, 44.9, 45.6, 85.5, 177.1, 208.7; MS (EI) m/z
(%) 213 (MH+, 100), 195 (10), 153 (20); HRMS calcd for (M+) C12H20O3: 212.1412;
found: 212.1409.
8.5 Compounds Described in Chapter 5.
The Synthesis of Cyclopentene (119b) from 1,2-Dioxine (1b) and Ylide (34e).
123
(±±±±) 1-Adamantyl (1S,2R,5R)-2-hydroxy-2,5-diphenyl-3-cyclopentene-1-
carboxylate (119b). A stirred solution of 1,2-dioxine (1b) (50 mg, 0.21 mmol) and
ylide (34e) (99 mg, 0.21 mmol) and lithium bromide (50 mg, 0.58 mmol) in toluene (1
ml) was immersed in an oil bath heated to 130°C. After 1 hour at 110°C the solution
was cooled and the solvent removed under a stream of nitrogen. The residue was
taken up in CH2Cl2 (20 ml) and washed with water (20 ml) then dried and
concentrated in vacuo. Purification by flash chromatography afforded 1,2-diketone
(36b) (11 mg, 22%) and colorless crystals of (119b) (11 mg, 12%); mp 180-182 °C
(hexane/ethyl acetate); Rf 0.30 (CH2Cl2); IR (nujol): 3430, 1696, 1248, 1184 cm-1; 1H
NMR (600 MHz) δ 1.61 (m, 6H), 2.06 (m, 6H), 2.11 (br s, 3H), 3.05 (d, J = 9 Hz,
1H), 3.41 (br s, 1H), 4.54 (ddd, J = 9.0, 2.4, 1.8 Hz, 1H), 5.98 (dd, J = 5.4, 2.4 Hz,
1H), 6.15 (dd, J = 5.4, 1.8 Hz, 1H), 7.22-7.25 (m, 4H), 7.26-7.37 (m, 4H), 7.50-7.52
(m, 2H); 13C NMR (75 MHz) δ 30.7, 36.1, 41.2, 52.5, 65.8, 81.7, 86.6, 125.4, 126.9,
127.0, 127.5, 128.0, 128.6, 136.5, 137.9, 142.8, 145.6, 171.8; MS (EI) m/z (%): 414
(10), 396 (20), 352 (40), 135 (100); Anal. Calcd for C26H30O3: C, 81.12; H, 7.29;
Found: C, 81.35; H, 7.50.
Crystallography for (119b). Intensity data for a colourless block (0.08 x 0.24 x 0.29
mm) were collected at 173 K employing Mo-Kα radiation (λ 0.7107 Å) and the ω:20
scan technique such that θmax was 27.5°. Corrections were made for Lorentz and
polarisation effects but not for absorption. Of the 4260 reflections measured, 3811
were unique (Rint = 0.051) and of these, 2372 satisfied the I ≥ 2.0σ(I) criterion.
Crystal data: C28H30O3, M = 414.5, monoclinic, P21/c, a = 12.757(4), b = 9.738(3), c =
17.633(5) Å, β = 98.51(2)°, V = 2166(1) Å3, Z = 4, Dx = 1.271, μ( Mo-Kα) F(000) =
888, 281, refined parameters, ρ = 0.20 e Å-3.
Rearrangement of Cyclopropane (91b) with Sodium Hydride. To a stirred solution
of sodium hydride in parrafin oil (10 mg, 55%, 0.23 mmol) dissolved in dry THF (1
ml) was added cyclopropane (91b) (60 mg, 0.14 mmol). An immediate colour change
from colourless to brown occurred upon addition of the cyclopropane. The solution
was stirred for 15 minutes and then quenched with water (10 ml). The mixture was
extracted with CH2Cl2 (2 × 20 ml). The organic extracts were dried and concentrated
in vacuo. The crude NMR showed resonances due to (119b) and (150) and another
124
unidentified product thought to be (149b). This crude mixture was redissolved in THF
(1 ml) and excess sodium hydride (70 mg) was added. After repeating the above
workup, the crude NMR showed only (119b) and (150). Purification by flash
chromatography afforded (119b) (11 mg, 18%) and (150) (21 mg, 35%)
1-Adamantyl 3,6-diphenyl-6-oxo-3-hexenoate (150). Colourless oil; Rf 0.45
(CH2Cl2); IR (neat): 3054, 2912, 1722, 1690, 1596, 1445, 1253, 1056 cm-1; 1H NMR
(300 MHz) δ 1.58-1.59 (m, 6H), 2.00 (br s, 6H), 2.10 (br s, 3H), 3.48 (s, 2H), 3.98 (d,
J = 6.6 Hz, 2H), 6.30 (t, J = 6.6 Hz, 1H) 7.24-7.58 (m, 8H), 8.00-8.03 (m, 2H); 13C
NMR (75 MHz) δ 30.7, 36.1, 38.4, 38.8, 41.6, 81.1, 123.4, 126.2, 127.1, 128.2, 128.3,
128.6, 133.1, 136.1, 136.7, 142.0, 169.8, 197.3; MS (EI) m/z (%): 414 (M+, 30), 413
(100); HRMS calcd for C28H30O3: 414.2194; found, 414.2181.
General procedure for the LHMDS Induced Ring-expansion of Cyclopropanes.
To a stirred solution of hexamethyldisilazane (2.1 mmol) in THF (5 ml) was added
methyl lithium (1.5 - 2.0 mmol) in diethyl ether. Stirring was continued for 10
minutes and then the cyclopropane (1 mmol) dissolved in THF (5 ml) was added
dropwise over 2 minutes. The reaction mixture was left to stir for 15 minutes and then
quenched with methanol (0.5 ml) and the the volatiles removed in vacuo. The product
was purified by flash chromatography / recrystallisation.
(±±±±) 1-Adamantyl (1S,2R,5R)-2-hydroxy-2,5-diphenyl-3-cyclopentene-1-
carboxylate (119b). The reaction of LHMDS (0.16 mmol) in THF (2 ml) and
cyclopropane (91b) (42 mg, 0.04 mmol) in THF (2 ml) as per the general procedure
gave (119b) as colourless crystals (35 mg, 83%).
(±±±±) tert-Butyl (1S,2R,5R)-2-hydroxy-5-methyl-2-phenyl-3-cyclopentene
carboxylate (147f). The reaction of LHMDS (0.5 mmol) in diethyl ether (2.5 ml) and
cyclopropane (82f) (95 mg, 0.34 mmol) after flash chromatography gave colourless
crystals of (147f); mp 85-87 °C; Rf 0.28 (CH2Cl2); IR (nujol): 3423, 1711, 1184, 1086
cm-1; 1H NMR (300 MHz) δ 1.20 (d, J = 7.0 Hz, 3H), 2.41 (s, 9H), 2.65 (d, J = 7.4
Hz, 1H), 3.32 (dddq, J = 7.4, 7.0, 2.5, 1.8 Hz, 1H), 3.75 (br s, 1H), 5.76 (dd, J = 5.6,
2.5 Hz, 1H), 5.98 (dd, J = 5.6, 1.8 Hz, 1H), 7.25-7.27 (m, 1H), 7.32-7.37 (m, 2H),
7.43-7.46 (m, 2H); 13C NMR (75 MHz) δ 19.4, 28.0, 42.1, 64.0, 81.4, 86.5, 125.2,
125
126.8, 127.9, 134.2, 139.9, 146.1, 172.3; MS (EI) m/z (%): 273 (M+-H, 3), 257 (100),
201 (50); Anal. Calcd for C17H22O3: C, 74.42; H, 8.08; Found: C, 74.53; H, 8.12.
(±±±±) tert-Butyl (E)-3-methyl-6-phenyl-6-oxo-4-hexenoate (149f). Colourless oil; Rf
0.27 (CH2Cl2); IR (neat): 2976, 1727, 1671, 1621, 1367, 1156 cm-1; 1H NMR (600
MHz) δ 1.17 (d, J = 6.9 Hz, 3H), 1.43 (s, 9H), 2.32 (dd, J = 14.8 Hz, 1H), 2.40 (dd, J
= 15.3, 7.0 Hz, 1H), 2.93 (dddq, J = 7.0, 7.0, 6.9, 6.9 Hz, 1H), 6.90 (d, J = 15.6 Hz,
1H), 6.98 (d, J = 15.6 Hz, 1H), 7.42-7.61 (m, 3H), 7.90-7.96 (m, 2H); 13C NMR (75
MHz) δ 19.2, 28.0, 33.8, 41.8, 80.7, 124.5, 128.5, 128.5, 132.6, 137.8, 152.5, 171.6,
190.9; MS (LSI) m/z (%): 275 (MH+, 5), 213 (100); Anal calcd for C17H22O3: C,
74.42; H, 8.08; Found: C, 74.18; H, 7.89.
(±±±±) tert-Butyl (1S,2R,5R)-2-hydroxy-2,5-diphenyl-3-cyclopentene-1-carboxylate
(147b). The reaction of LHMDS (2.67 mmol) in THF (10 ml) with tert-butyl 2-(2-
oxo-2-phenylethyl)-3-phenylcyclopropane-1-carboxylate (82b) (600 mg, 1.78 mmol)
in THF (10 ml) as per the general procedure afforded (147b) as colourless crystals
(481 mg, 80%); mp 127-128 °C (hexane); Rf 0.26 (CH2Cl2); IR (nujol): 3450, 1707,
1251, 1160 cm-1; 1H NMR (300 MHz) δ 1.35 (s, 9H), 3.06 (d, J = 7.7, 1H), 3.37 (br s,
1H), 4.56 (ddd, J = 7.7, 2.5, 1.9 Hz, 1H), 5.99 (dd, J = 5.8, 2.5 Hz, 1H), 6.17 (dd, J =
5.8, 1.9 Hz, 1H), 7.21-7.39 (m, 8H), 7.50-7.53 (m, 2H); 13C NMR (75 MHz) δ 28.0,
52.4, 65.9, 81.5, 86.7, 125.3, 126.8, 127.0, 127.3, 128.0, 128.6, 136.5, 137.9, 142.7,
145.5, 171.3; MS (EI) m/z (%): 336 (M+, trace), 318 (12), 280 (30), 218 (100); Anal.
Calcd for C22H24O3: C, 78.54; H, 7.19; Found: C, 78.58; H, 7.15.
(±±±±) 1-Adamantyl (1S,2R)-2-hydroxy-2-phenyl-3-cyclopentene-1-carboxylate
(119c). The reaction of LHMDS (0.22 mmol) in diethyl ether (2 ml) and cyclopropane
(91c) (50 mg, 0.15 mmol) in diethyl ether (2 ml) as per the general procedure afforded
(119c) as colourless rods (43 mg, 85%); mp 142-143 °C (hexane); Rf 0.28 (CH2Cl2);
IR (nujol): 3423, 1711, 1184, 1086 cm-1; 1H NMR (600 MHz) δ 1.64 (br s, 6H), 2.08-
2.14 (m, 6H), 2.14 (br s, 3H), 2.67 (dddd, J = 17.0, 8.6, 2.4, 1.8 Hz, 1H), 2.92 (dddd,
J = 17.0, 7.0, 2.4, 2.2 Hz, 1H), 3.17 (dd, J = 8.6, 7.0 Hz, 1H) 3.47 (br s, 1H), 5.80
(ddd, J = 5.8, 2.4, 1.8 Hz, 1H), 6.12 (ddd, J = 5.8, 2.4, 2.2 Hz, 1H), 6.91-7.31 (m, 1H),
7.33-7.43 (m, 2H), 7.43-7.47 (m, 2H); 13C NMR (75 MHz) δ 30.7, 34.7, 36.1, 41.3,
55.6, 81.4, 86.2, 125.2, 126.8, 127.9, 133.6, 136.0, 146.0, 172.2; MS (EI) m/z (%):
126
338 (M+, 20), 320 (10), 135 (100); Anal. Calcd for C22H26O3: C, 78.07; H, 7.74;
Found: C, 78.13; H, 7.58.
(±±±±) tert-Butyl (1S,2R,5R)-2-hydroxy-2,5-dipropyl-3-cyclopentene carboxylate
(147k). The reaction of LHMDS (0.35 mmol) in diethyl ether (2 ml) and
cyclopropane (82k) (50 mg, 0.19 mmol) in diethyl ether (2 ml) as per the general
procedure gave (147k) as a colourless oil (42 mg, 84%); Rf 0.40 (CH2Cl2); IR (neat):
3483, 2959, 1717, 1458, 1368 cm-1; 1H NMR (300 MHz) δ 0.91 (t, J = 7.2 Hz, 3H),
0.94 (t, J = 7.4 Hz, 3H), 1.20-1.50 (m, 6H), 1.44 (s, 9H), 1.65-1.72 (m, 2H), 2.47 (d, J
= 8.8, 1H), 2.54 (br s, 1H), 3.17 (m, 1H), 5.61 (dd, J = 5.6, 2.5 Hz, 1H), 5.79 (dd, J =
5.6, 2.5 Hz, 1H); 13C NMR (75 MHz) δ 14.1, 14.5, 17.8, 20.8, 28.1, 37.2, 43.0, 47.4,
58.2, 80.9, 86.1, 134.2, 137.0, 172.8; MS (EI) m/z (%): 251 (M+-OH, 10), 195 (20),
169 (50), 151 (70); Anal. Calcd for C16H28O3: C, 71.6; H, 10.51; Found: C, 71.55; H,
10.25.
(±±±±) (E) tert-Butyl 3-propyl-6-oxo-4-nonenoate (149k). Rf 0.40 (CH2Cl2); IR (neat):
2961, 1729, 1673, 1457, 1153 cm-1; 1H NMR (600 MHz) δ 0.89 (t, J = 7.2 Hz, 3H),
0.93 (t, J = 7.2 Hz, 3H), 1.20-1.50 (m, 6H), 1.42 (s, 9H), 1.63 (tq, J = 7.2, 7.2 Hz,
2H), 2.24 (dd, J = 15, 8.4 Hz, 1H) 2.35 (d, J = 15, 6.0 Hz, 1H), 2.63-2.67 (m, 1H),
6.09 (dd, J = 16, 0.8 Hz, 1H), 6.64 (dd, J = 16, 9.0 Hz, 1H); 13C NMR (75 MHz) δ
13.7, 13.8, 17.6, 20.0, 28.0, 36.1, 38.9, 40.4, 42.1, 80.5, 130.1, 148.8, 171.0, 200.4;
MS (LSI) m/z (%): 269 (MH+, 5), 213 (100); HRMS calcd for C16H29O3 : 269.2116;
found 269.2103.
(±±±±) tert-Butyl (1S,2S,5R)-2-hydroxy-5-methyl-2-phenyl-3-cyclopentene
carboxylate (148). To a stirred solution of KHMDS (0.5 mmol) in diethyl ether (3
ml) and toluene (0.7 ml) was added cyclopropane (82f) (50 mg, 0.34 mmol) in a
solution of toluene (0.5 ml). Purification by flash chromatography (CH2Cl2) then
recrystallisation from hexane gave (147f) (38 mg, 76%) and (148) as colourless
crystals (4 mg, 8%); mp 114-116 °C; Rf 0.25 (CH2Cl2); IR (nujol): 3472, 1686, 1162
cm-1; 1H NMR (600 MHz) δ 1.05 (s, 9H), 1.23 (d, J = 6.9 Hz, 3H), 2.66 (br s, 1H),
2.90 (d, J = 7.2 Hz, 1H), 3.32 (dddq, J = 7.2, 6.9, 2.3, 1.9 Hz, 1H), 5.66 (dd, J = 5.5,
2.3 Hz, 1H), 5.88 (dd, J = 5.5, 1.9 Hz, 1H), 7.19-7.43 (m, 5H); 13C NMR (75 MHz) δ
20.3, 27.5, 41.7, 52.6, 67.9, 80.6, 88.9, 125.2, 127.2, 128.0, 135.4, 137.1, 142.9, 170.3
127
; MS (EI) m/z (%): 274 (M+, 3), 256 (3), 218 (100), 200 (25); Anal. Calcd for
C17H22O3: C, 74.40; H, 8.08; Found: C, 74.53; H, 8.12
(±±±±) (E) tert-Butyl 4-methyl-6-phenyl-6-oxo-2-hexenoate (157). White solid; mp 35-
38 °C; Rf 0.53 (80:20 hexane/ethyl acetate); 1H NMR (600 MHz) δ 1.14 (d, J = 6.6
Hz, 3H), 1.47 (s, 9H), 2.94-3.12 (m, 4H), 5.78 (dd, J = 15.6, 1.5 Hz, 1H), 6.87 (dd, J
= 15.6, 6.6 Hz, 1H), 7.44-7.57 (m, 3H), 7.93-7.96 (m, 2H); 13C NMR (75 MHz) δ
19.1, 28.1, 31.7, 44.2, 80.2, 121.7, 128.1, 128.6, 133.1, 137.0, 151.4, 166.1, 198.1;
MS (EI) m/z (%): 274 (M+, 20), 218 (50), 200 (80), 157 (50), 104 (100); Anal. Calcd
for C17H22O3: C, 74.40; H, 8.08; Found: C, 74.18, H, 7.89.
(±) tert-Butyl (1S,4S,5R)-4-hydroxy-2,5-diphenyl-2-cyclopentene-1-carboylate
(158b). To a solution of cyclopentene (147b) (32 mg, 0.095 mmol) in CDCl3 (0.7 ml)
was added trifluoroacetic acid (14 mg, 0.12 mol). The reaction was monitored using 1H NMR and after all starting material had been consumed, (50 minutes) the mixture
was added to silica (≈ 0.5 g) and stirred for 10 minutes. The volatiles were removed in
vacuo and the product purified by flash chromatography to give (158b) as colourless
crystals (28 mg, 88%); mp 98-99 °C; Rf 0.33 (95:5 CH2Cl2/ethyl acetate); IR (neat)
3423, 2977, 1726, 1706, 1601, 1495, 1453, 1368, 1150, 698 cm-1; 1H NMR (200
MHz) δ 1.34 (s, 9H), 3.46 (d, J = 10.2 Hz, 1H), 3.49 (s, 1H), 3.95 (dd, J = 1.4, 1.4 Hz,
1H), 4.67 (ddd, J = 10.2, 2.6, 1.4 Hz, 1H), 6.50 (dd, J = 2.6, 1.4 Hz, 1H), 7.16-7.40
(m, 8H), 7.58-7.62 (m, 2H); 13C NMR (150 MHz) δ 27.7, 56.8, 58.8, 82.1, 83.4,
126.6, 126.7, 126.8, 128.4, 128.5, 128.7, 129.8, 133.9, 142.8, 145.2, 174.5; MS (EI)
m/z (%): 336 (10), 318 (40), 280 (20), 57 (100); Anal. calcd for C22H24O3: C, 78.54,
H, 7.19; Found: C, 78.54; H, 7.23.
(±±±±) tert-Butyl (1S,4S,5S)-4-hydroxy-5-methyl-2-phenyl-2-cyclopentene-1-
carboxylate (158f). To a solution of cyclopentene (147f) (24 mg, 0.086 mmol) in
CDCl3 (0.7 ml) was added trifluoroacetic acid (15 mg, 0.13 mmol). Analysis by 1H
NMR after 15 minutes showed that complete consumption of starting material had
occurred. Silica (≈0.5 g) was added to the solution, the volatiles were removed in
vacuo and the residue purified by flash chromatography to give (158f) as a colourless
oil (16.5 mg, 69%); Rf 0.40 (95:5 CH2Cl2/ethyl acetate); IR (neat) 3417, 2975, 1714,
1151 cm-1; 1H NMR (300 MHz) δ 1.34 (d, J = 7.5 Hz, 3H), 1.35 (s, 9H) 2.39 (q, J =
128
7.5 Hz, 1H), 3.26 (br s, 1H), 3.40 (dd, J = 1.2, 1.2 Hz, 1H), 4.32 (br s, 1H), 6.40 (d, J
= 1.2 Hz, 1H), 7.27-7.37 (m, 3H), 7.52-7.55 (m, 2H); 13C NMR (150 MHz) δ 19.3,
27.8, 45.9, 58.8, 81.8, 82.9, 126.5, 128.3, 128.3, 129.3, 134.4, 144.0, 175.1; MS (EI)
m/z (%): 274 (3), 218 (40), 172 (40), 57 (100); HRMS calcd for C17H22O3: 274.1568;
found, 274.1569.
m-CPBA Epoxidation of Cyclopentene (147b). To a stirred solution of cyclopentene
(147b) (175 mg, 0.52 mmol) in CH2Cl2 (3 ml) was added 70% m-CPBA (192 mg,
0.78 mmol). The reaction mixture was stirred for 24 hours then concentrated in vacuo
and analysed by 1H NMR. Purification by flash chromatography gave a (56:44)
mixture of the two crystalline products (163) and (164) (159 mg, 87%) that were
further separable by recrystallisation (CH2Cl2/hexane) affording the following
epoxides:
(±±±±) tert-Butyl (1aS,2R,4R,4aS)-2-hydroxy-2,4-diphenyltetrahydro-1aH-
cyclopenta[b]oxirene-2-carboxylate (163). Colorless crystals; mp 136-138 oC
(CH2Cl2/hexane); Rf 0.40 (CH2Cl2); IR (nujol): 3403, 1704, 1496, 1271, 1236, 1162
cm-1; 1H NMR (300 MHz) δ 1.16 (s, 9H), 2.93 (d, J = 10.8 Hz, 1H), 3.66 (d, J = 2.7
Hz, 1H), 3.68 (dd, J = 10.5, 1.2 Hz, 1H), 3.79 (dd, J = 2.7, 1.2 Hz, 1H), 4.90 (s, 1H),
7.23-7.60 (m, 8H), 7.64-7.67 (m, 2H); 13C NMR (75 MHz) δ 27.7, 48.8, 56.1, 58.6,
60.5, 80.2, 82.3, 125.1, 127.3, 127.6, 128.1, 128.2, 128.5, 138.8, 142.4, 173.0; MS
(EI) m/z (%): 352 (M+, 4), 296 (20), 233 (30), 173 (30), 105 (100); Anal. Calcd for
C22H24O4: C, 74.97; H, 6.86; Found: C, 75.10; H, 7.04.
(±±±±) tert-Butyl (1aR,2R,4R,4aR)-2-hydroxy-2,4-diphenyltetrahydro-1aH-
cyclopenta[b]oxirene-2-carboxylate (164). Colourless crystals; mp 81-83 oC
(CH2Cl2/hexane); Rf 0.35 (CH2Cl2); IR (nujol): 3445, 1722, 1233, 1155, 741, 702 cm-
1; 1H NMR (200 MHz) δ 1.36 (s, 9H), 3.45 (d, J = 7.4 Hz, 1H), 3.59 (s, 1H), 3.89 (dd,
J = 2.4, 0.6 Hz, 1H), 3.90 (d, J = 2.4 Hz, 1H), 4.06 (d, J = 7.4 Hz, 1H), 7.25-7.40 (m,
8H), 7.55-7.59 (m, 2H); 13C NMR (75 MHz) δ 28.0, 48.1, 64.6, 67.8, 68.7, 80.4, 81.3,
125.0, 127.1, 127.4, 127.6, 128.3, 128.9, 140.9, 143.5, 169.8; MS (EI) m/z (%): 352
(M+, 10), 296 (30), 161 (100); Anal. Calcd for C22H24O4: C, 74.97; H, 6.86; Found: C,
75.23; H, 6.97.
129
8.6 Compounds Described in Chapter 6.
General procedure for the synthesis of THFs from 1,2-dioxine precursors. To
3,6-diphenyl-3,6-dihydro-1,2-dioxine 2a (238 mg, 1 mmol) in THF (5 ml) was added
lithium hydroxide (23 mg, 1 mmol) and the resulting suspension stirred for 16 hours.
The mixture was concentrated in vacuo and the products separated by flash
chromatography (60:40 hexane/ethyl acetate) to afford the following:
(±) 2-{(2S,3S,4S,5S)-4-Benzoyl-5-[(S)-1-hydroxy-1-phenylmethyl]-2-
phenyltetrahydro-3-furanyl}-1-phenyl-1-ethanone (171b). White solid; mp 150-
152 °C; Rf 0.38 (60:40 hexane/ethyl acetate); IR (nujol) 3411, 1683, 1667, 1043 cm-1; 1H NMR (600 MHz) δ 2.89 (d, J = 3.0 Hz, 1H), 3.00-3.07 (m, 2H), 3.15-3.19 (m, 1H),
4.11 (dd, J = 8.4, 6.6 Hz, 1H), 4.69 (dd, J = 7.2, 6.6 Hz, 1H), 4.78 (dd, J = 7.2, 3.0 Hz,
1H), 4.96 (d, J = 3.6 Hz, 1H), 7.12-7.37 (m, 13H), 7.44-7.48 (m, 5H), 7.59-7.61 (m,
2H); 13C NMR (150 MHz) δ 38.1, 50.1, 53.1, 75.6, 85.6, 87.4, 127.2, 127.5, 127.8,
128.1, 128.2, 128.4, 128.5, 128.5, 128.6, 132.7, 133.2, 136.5, 136.9, 138.9, 139.5,
197.9, 199.7 (1 masked aromatic); MS (EI) m/z (%): 477 (M+, 5), 459 (25), 369 (80),
221 (100). (171b) was converted to its acetate (172b) for comparison with literature
data. (171b) (36 mg, 0.075 mmol) was dissolved in dichloromethane (1 ml) and acetyl
chloride (12 mg, 0.15 mmol) was added. Pyridine (1 drop) was added and the reaction
left to stir overnight. Evaporation of the volatiles in vacuo and purification by flash
chromatography then recrystallisation from hot hexane afforded a white solid (172b)
(14 mg, 36%): mp 190-192 °C, lit14 193-194 °C; Spectral data was consistent with
that reported.
(±) 2-{(2S,3S,4R,5R)-4-Benzoyl-5-[(R)-1-hydroxy-1-phenylmethyl]-2-
phenyltetrahydro-3-furanyl}-1-phenyl-1-ethanone (173b). White Solid; mp 140-
142 °C; Rf 0.56 (60:40 hexane/ethyl acetate); IR (nujol) 1681, 1672, 1237, 1047, 1023
cm-1; 1H NMR (600 MHz) δ 2.84 (dd, J = 18.0, 4.2 Hz, 1H), 3.06 (br s, 1H), 3.10-3.16
(m, 1H), 3.24 (dd, J = 18.0, 10.2 Hz, 1H), 4.48 (dd, J = 7.8, 4.8 Hz, 1H), 4.51 (dd, J =
7.8, 4.8 Hz, 1H), 4.88 (d, J = 7.8 Hz, 1H), 5.12 (d, J = 9.6Hz, 1H), 7.12-7.58 (m,
18H), 7.58-7.60 (m, 2H); 13C NMR (75 MHz) δ 35.8, 46.7, 49.0, 77.2, 77.3, 86.4,
126.9, 127.5, 127.6, 128.2, 128.2, 128.3, 128.4, 128.6, 128.7, 133.0, 136.4, 136.6,
139.5, 139.7, 198.3, 201.2 (2 masked aromatic); MS (EI) m/z (%): 477 (M+, 10), 459
130
(40), 440 (30), 369 (95), 105 (100); Anal. Calcd for C32H28O4: C, 80.65; H, 5.92;
Found: C, 80.21; H, 5.98. (173b) (81 mg, 0.17 mmol) was converted to its
corresponding acetate for X-ray diffraction studies as per (171b) to give (179) as
colourless crystals (46 mg, 52%): mp 184-186 °C; Rf 0.30 (80:20 hexane/ethyl
acetate); IR (nujol) 1743, 1670, 1591, 1576, 1232, 1207 cm-1; 1H NMR (300 MHz) δ
2.08 (s, 3H), 2.81 (dd, J = 17.7, 7.2 Hz, 1H), 3.03 (dddd, J = 10.2, 7.2, 8.7, 4.5 Hz,
1H), 3.12 (dd, J = 17.7, 10.2 Hz, 1H), 4.44 (dd, J = 8.4, 5.4 Hz, 1H), 4.78 (dd, J = 6.0,
6.0 Hz, 1H), 5.02 (d, J = 8.7 Hz, 1H), 6.09 (d, J = 6.9 Hz, 1H), 7.16-7.57 (m, 20H); 13C NMR (75 MHz) δ 21.1, 35.8, 47.1, 49.1, 77.3, 83.7, 86.1, 126.9, 127.5, 127.8,
128.2, 128.3, 128.5, 133.0, 133.1, 136.4, 136.8, 136.8, 139.8, 170.1, 198.2, 201.4 (4
masked aromatics); MS (EI) m/z (%): 518 (M+, 5), 517 (10), 501 (30), 440 (50), 369
(100); Anal. Calcd for C34H30O5: C, 78.74; H, 5.83; Found: C, 78.72; H, 5.85.
(±) 2-[(3S,4S,5S)-4-Benzoyl-5-(hydroxymethyl)tetrahydro-3-furanyl]-1-phenyl-1-
ethanone (171c). Colourless oil; Rf 0.30 (50:50 hexane/ethyl acetate); IR (neat) 3459,
2874, 1681, 1596, 1448, 1213 cm-1; 1H NMR (600 MHz) δ 2.21 (br s, 1H), 3.17 (dd, J
= 17.4, 8.4 Hz, 1H), 3.1 (dd, J = 17.4, 6.0 Hz, 1H), 3.35 (m, 1H), 3.57 (br d, J = 12.0
Hz, 1H), 3.78 (dd, J = 9.0, 5.4 Hz, 1H), 3.86 (dd, J = 12.0, 3.0 Hz, 1H), 3.96 (dd, J =
7.8, 6.6 Hz, 1H), 4.14 (ddd, J = 8.4, 3.0, 3.0 Hz, 1H), 4.30 (dd, 8.4, 7.2 Hz, 1H), 7.40-
7.43 (m, 2H), 7.46-7.49 (m, 2H), 7.52-7.55 (m, 1H), 7.57-7.60 (m, 1H), 7.86-7.87 (m,
2H), 7.99-8.01 (m, 2H); 13C NMR (150 MHz) δ 40.7, 41.9, 52.1, 62.3, 73.6, 83.5,
127.9, 128.5, 128.6, 128.8, 133.2, 133.5, 136.4, 137.1, 198.2, 199.9; MS (EI) m/z (%):
325 (MH+, 15), 305 (20), 145 (40),105 (100); HRMS of (MH+) C20H21O4: calcd,
325.1439; found: 325.1434. To a stirred solution of THF (171c) (55 mg, 0.16 mmol)
dissolved in CH2Cl2 (1.5 ml) was added acetyl chloride (26 mg, 0.33 mmol) followed
by pyridine (1 drop). The resulting solution was stirred for 3 hours and then the
volatiles removed under a stream of nitrogen gas. The residue was dissolved in
CH2Cl2 (1 ml) and purified by flash chromatography (60:40 hexane/ethyl acetate) to
give the acetate as a colourless oil (42 mg, 68%); IR (neat) 2952, 1742, 1681, 1596,
1580, 1448, 1369, 1239 cm-1; 1H NMR (300 MHz) δ 1.93 (s, 3H), 3.23-3.29 (m, 3H),
3.72-3.82 (m, 2H), 4.14-4.37 (m, 4H), 7.40-7.63 (m, 6H), 7.85-7.96 (m, 4H); 13C
NMR (75 MHz) δ 20.6, 40.9, 41.8, 53.7, 64.9, 73.6, 80.5, 127.8, 128.3, 128.6, 128.8,
133.3, 133.5, 136.3, 136.8, 170.6, 198.0, 199.4; MS (EI) m/z (%): 367 (MH+, 10), 349
(10), 105 (100).
131
(±) 2-[(3S,4R,5R)-4-Benzoyl-5-(hydroxymethyl)tetrahydro-3-furanyl]-1-phenyl-1-
ethanone (173c). Colourless oil; Rf 0.29 (ethyl acetate); IR (neat) 3402, 2918, 1680,
1596, 1448, 1379, 1219 cm-1; 1H NMR (600 MHz) δ 1.90 (br s, 1H), 2.88 (dd, J =
17.9, 5.1 Hz, 1H), 3.11 (dd, J = 17.9, 9.7 Hz, 1H), 3.37 (m, 1H), 3.62 (dd, J = 11.9,
4.0 Hz, 1H), 3.77 (dd, J = 8.9, 5.5 Hz, 1H), 3.87 (dd, J = 11.9, 3.6 Hz, 1H), 4,29 (dd, J
= 8.1, 8.1 Hz, 1H), 4.33 (dd, J = 8.7, 6.2 Hz, 1H), 4.54 (ddd, J = 8.1, 4.0, 3.6 Hz, 1H),
7.36-7.58 (m, 6H), 7.76-7.77 (m, 2H), 7.98-8.00 (m, 2H); 13C NMR (150 MHz) δ
37.6, 39.1, 49.3, 63.3, 74.2, 81.1, 127.8, 128.3, 128.5, 128.8, 133.2, 133.7, 136.5,
137.0, 198.2, 199.6; MS (EI) m/z (%): 325 (MH+, 15), 305 (20), 145 (40),105 (100);
HRMS calcd for (MH+) C20H21O4: calcd, 325.1439; found: 325.1449.
(±) 2-[(3R,3aR,4R,6aS)-4-hydroxy-4-phenylperhydrofuro[3,4-b]furan-3-yl]-1-
phenyl-1-ethanone (174c). Although stable as a solid (174c) slowly decomposed in
CDCl3 solution; White solid; mp 134-135 °C; Rf 0.50 (ethyl acetate); IR (nujol) 3384,
1678, 1596, 1265, 1228 cm-1; 1H NMR (600 MHz) δ 2.08 (m, 1H), 2.53 (s, 1H), 2.59
(dd, J = 16.2, 10.2 Hz, 1H), 2.80 (dd, J = 16.2, 5.1 Hz, 1H), 2.80 (dd, J = 6.6, 6.6 Hz,
1H), 3.36 (dd, J = 9.0, 6.6 Hz, 1H), 3.62 (dd, J = 9.0, 6.0 Hz, 1H), 4.12 (d, J = 10.2
Hz, 1H), 4.27 (dd, J = 10.2, 4.5 Hz, 1H), 4.88 (dd, J = 6.6, 4.5 Hz, 1H), 7.32-7.54 (m,
8H), 7.65-7.68 (m, 2H); 13C NMR (150 MHz) δ 39.5, 41.2, 59.9, 72.4, 73.5, 83.5,
107.8, 126.5, 127.9, 128.3, 128.5, 128.6, 128.9, 133.0, 140.6, 189.5; MS (EI) m/z (%):
306 (M+-H2O, 5), 288 (20), 168 (10), 105 (100); Anal. Calcd for C20H20O4: C, 74.05;
H, 6.21; Found: C, 73.80; H, 6.21.
(±) 2-{(2S,3R,4R,5R)-4-Benzoyl-5-[(1R)-1-hydroxyethyl]-2-methyltetrahydro-3-
furanyl}-1-phenyl-1-ethanone (171f). Colourless oil; Rf 0.21 (60:40 hexane/ethyl
acetate); IR (neat) 3468, 2973, 1681, 1596, 1448, 1366, 1265, 1214, 1074 cm-1; 1H
NMR (600 MHz, C6D6) δ 1.07 (d, J = 6.0 Hz, 3H), 1.35 (d, J = 6.6 Hz, 3H), 1.80-2.20
(br s, 1H), 2.72-2.73 (m, 2H), 3.16 (dddd, J = 8.4, 7.6, 6.8, 6.8 Hz, 1H), 3.61 (dq, J =
6.6, 3.3 Hz, 1H), 3.98 (dq, J = 7.6, 6.0 Hz, 1H), 4.15 (dd, J = 8.2, 8.4 Hz, 1H), 4.23
(dd, J = 8.2, 3.3 Hz, 1H), 7.01-7.13 (m, 6H), 7.67-7.69 (m, 2H), 8.12-8.14 (m, 2H); 13C NMR (150 MHz, CDCl3) δ 19.8, 19.9, 40.5, 48.2, 54.1, 68.1, 80.8, 85.7, 127.9,
128.4, 128.5, 128.6, 133.2, 133.3, 136.5, 137.4, 198.1, 200.0; MS (EI) m/z (%): 353
(M+, 8), 335 (10), 307 (20),159 (100). (171f) was converted to its acetate (178) for X-
132
ray diffraction studies. (171f) (83 mg, 0.23 mmol) was treated as per (171b) to give
colourless crystals of (178) (69 mg, 74%): mp 99-101 °C (CH3CN / H2O); Rf 0.38
(60:40 hexane/ethyl acetate); IR (nujol) 1741, 1683, 1667, 1596, 1246, 1216 cm-1; 1H
NMR (300 MHz, C6D6) δ 1.21 (d, J = 6.6 Hz, 3H), 1.36 (d, J = 6.0 Hz, 3H), 2.00 (s,
3H), 2.85 (dddd, J = 8.5, 8.2, 7.4, 5.8 Hz,1H), 3.05 (dd, J = 16.7, 7.4 Hz, 1H), 3.16
(dd, J = 16.7, 5.8 Hz, 1H), 3.89 (dd, J = 6.6, 8.5 Hz, 1H), 4.09 (dq, J = 8.2, 6.0 Hz,
1H), 4.28 (dd, J = 7.2, 4.7 Hz, 1H), 5.00 (dq, J = 6.6, 4.7 Hz, 1H), 7.37-7.45 (m, 4H),
7.51-7.56 (m, 2H), 7.75-7.79 (m, 2H), 7.88-7.91 (m, 2H); 13C NMR (75 MHz, CDCl3)
δ 16.1, 19.3, 21.1, 39.9, 48.2, 53.8, 70.9, 80.7, 83.2, 127.9, 128.3, 128.6, 128.7, 131.1,
133.2, 136.6, 137.2, 170.3, 198.0, 199.8; MS (EI) m/z (%): 395 (MH+, 10), 335 (10),
159 (95), 105 (100); Anal. Calcd for C24H26O5: C, 73.07; H, 6.64; Found: C, 72.93; H,
6.77.
(±) 2-[(2R,3S,3aS,4S,6S,6aR)-4-Hydroxy-2,6-dimethyl-4-phenylperhydrofuro[3,4-
b]furan-3-yl]-1-phenyl-1-ethanone (174f) White solid; mp 148-150 °C; Rf 0.50
(60:40 hexane/ethyl acetate); IR (neat) 3368, 2924, 1673, 1595, 1320, 1267 cm-1; 1H
NMR (600 MHz) δ 0.95 (d, J = 6.0 Hz, 3H), 1.33 (d, J = 6.6 Hz, 3H), 1.59 (dddd, J =
9.6, 9.2, 8.2, 3.6 Hz, 1H), 2.43 (dd, J = 15, 9.6 Hz, 1H), 2.71 (s, 1H), 2.74 (dd, J = 15,
3.6 Hz, 1H), 2.89 (dd, J = 8.2, 7.6 Hz, 1H), 3.64 (dq, J = 9.2, 6.0 Hz, 1H), 4.36 (dq, J
= 6.6, 4.8 Hz, 1H), 4.58 (dd, J = 7.6, 4.8 Hz, 1H), 7.01-7.13 (m, 6H), 7.67-7.69 (m,
2H), 8.12-8.14 (m, 2H); 13C NMR (150 MHz) δ 13.75, 18.6, 40.8, 46.3, 62.1, 75.3,
81.2, 83.2, 106.2, 126.8, 128.0, 128.3, 128.4, 128.5, 132.9, 136.3, 140.8, 198.7; MS
(EI) m/z (%): 335 (MH+-H2O, 8), 316 (15), 290 (20),105 (100); Anal. Calcd for
C22H24O4: C, 74.97; H, 6.86; Found: C, 74.72; H, 6.70.
(±) 2-{(2R,3R,4R,5R)-4-Benzoyl-5-[(1S)-1-hydroxyethyl]-2-methyltetrahydro-3-
furanyl}-1-phenyl-1-ethanone (175). Isolated as a 75:25 mixture together with an
unidentified isomer not separable by chromatography as a colourless oil; Rf 0.33
(60:40 hexane/ethyl acetate); 1H NMR (300 MHz, C6D6) δ 1.00 (d, J = 6.6 Hz, 3H),
1.02 (d, J = 6.6 Hz, 3H), 2.00 (br d, J = 7.5 Hz, 1H), 2.74-2.90 (m, 2H), 3.44 (dq, J =
6.6, 5.7 Hz, 1H), 3.56 (br m, 1H), 3.99-4.06 (m, 2H), 4.56 (dq, J = 8.4, 6.6 Hz, 1H)
6.89-7.16 (m, 6H), 7.73-7.76 (m, 2H), 8.13-8.17 (m, 2H); 13C NMR (150 MHz) δ
16.7, 20.3, 38.1, 43.6, 52.8, 67.7, 76.8, 85.9, 127.9, 128.5, 128.5, 128.7, 133.2, 133.4,
136.6, 137.2, 198.4, 200.7; MS (EI) m/z (%): 334 (MH+-H2O, 20), 307 (30), 159 (90),
133
105 (100). (175) (46 mg, 0.19 mmol) was converted to its corresponding acetate as
per (171b) to give a colourless oil as a single isomer (38 mg, 75%); IR (neat) 2980,
1732, 1682, 1597, 1448, 1372, 1242; 1H NMR (600 MHz, C6D6) δ 1.24 (d, J = 6.0 Hz,
3H), 1.25 (d, J = 6.0 Hz, 3H), 1.91 (s, 3H), 3.00 (dd, J = 16.8, 8.4 Hz, 1H), 3.06-3.10
(m, 1H), 3.30 (dd, J = 16.8, 6.0 Hz, 1H), 3.75 (dd, J = 6.6, 4.2 Hz, 1H), 4.17 (dd, J =
7.2, 4.2 Hz, 1H), 7.41-7.47 (m, 4H) 7.53-7.58 (m, 2H), 7.87-7.89 (m, 4H); LSIMS m/z
(%): 395 (MH+, 90), 393 (100), 377 (20), 215 (90); HRMS of (MH+) C24H27O5: calcd,
395.1858; found: 395.1864.
X-ray Crystallography for (178) and (179). Intensity data for colourless crystals of
(178) and (179) were measured at 223(2) K on a Bruker AXS SMART CCD using
Mo Kα radiation so that θmax = 30.0 and 30.1°, respectively. The structures were
solved by direct-methods and refined (anistropic displacement parameters, H atoms in
their calculated positions and a weighting scheme w = 1/[σ2(Fo2) + aP2 + bP] where P
= (Fo2 + 2Fc
2)/3; (178): a = 0.0975, b = 1.2404); (179): a = 0.0885, b = 3.2162 on F2
with SHELXL-97. While not optimal, the structures have been determined
unambiguously. The molecular structures (ORTEP, 50% displacement parameters)
are shown in Figs 1 and 2.
Crystal data for (178): C24H26O5, M = 394.5, monoclinic, P21/c, a = 11.5612(11), b =
10.9672(11), c = 17.5001(18) Å, β = 108.290(2) °, V = 2106.8(4) Å3, Z = 4, Dx =
1.244, F(000) = 840, μ = 0.086 mm-1, no. of unique data = 6095, no. of parameters =
262, R (all data) = 0.100, wR (all data) = 0.209, ρ = 0.57 e Å-3.
Crystal data for (179): C34H30O5, M = 518.6, monoclinic, C2/c, a = 19.9779(14), b =
13.9738(10), c = 19.1132(14) Å, β = 96.462(2) °, V = 5301.9(7) Å3, Z = 8, Dx = 1.299,
F(000) = 2192, μ = 0.086 mm-1, no. of unique data = 7731, no. of parameters = 352, R
(all data) = 0.087, wR (all data) = 0.177, ρ = 0.50 e Å-3.
(±±±±) 5-Ethyl-7-hydroxy-3-(1-hydroxybutyl)-1,6-dipropyl-1,3,3a,4,7,7a-hexahydro-
4-isobenzofuranone (176). Colourless oil; Rf 0.10 (60:40 hexane/ethyl acetate); IR
(neat) 3429, 2959, 1651, 1463, 1378, 1063 cm-1; 1H NMR (600 MHz) δ 0.92-0.99 (m,
9H), 1.01 (t, J = 7.2 Hz, 3H), 1.36-1.60 (m, 12H), 2.28-2.38 (m, 4H), 2.42 (ddd, J =
8.4, 8.4, 4.2 Hz, 1H), 3.02 (dd, J = 8.4, 5.4 Hz, 1H), 3.58 (ddd, J = 13.8, 4.2, 4.2 Hz,
1H), 3.61 (ddd, J = 7.8, 7.8, 4.2 Hz, 1H), 3.80 (dd, J = 5.4, 4.2 Hz, 1H), 4.17 (d, J =
4.2 Hz, 1H); 13C NMR (75 MHz) δ 13.7, 14.0, 14.0, 14.4, 18.8, 19.0, 19.3, 21.7, 34.1,
134
36.1, 36.9, 48.1, 50.8, 66.7, 72.6, 81.4, 84.1, 138.4, 155.4, 197.5; MS (EI) m/z (%):
339 (MH+, 40), 321 (10), 265 (10), 220 (100).
The Synthesis of trans-γγγγ-Hydroxyenones.
(E)-4-Hydroxy-1,4-diphenyl-2-buten-1-one (38b).50 To a stirred solution of
Co(II)(SALEN)2 (10 mg) dissolved in CH2Cl2 (5 ml) was added 3,6-diphenyl-3,6-
dihydro-1,2-dioxine (1b) (238 mg, 1.0 mmol). The resulting solution was stirred for
30 minutes and then triphenylphosphine (132 mg, 0.5 mmol) was added in one
portion. The solution was stirred for an additional hour and then the volatiles removed
in vacuo. Purification by flash chromatography (florisil®) afforded (38b) as a
colourless oil (160 mg, 68%); Rf 0.40 (60:40 hexane/ethyl acetate).
General Procedure for the Synthesis of trans-γγγγ-Hydroxyenones (38c,i,n-q). To a
solution of the appropriate stabilised ylide (182) (3.6 mmol, 1.2 mol. equiv.) in THF
(15 ml) was added glycoaldehyde dimer (180 mg, 1.50 mmol, 1.0 mol. equiv.) and the
resulting solution heated under reflux for 3 hours. The solution was cooled and the
solvent removed in vacuo. The product was purified by chromatography (florisil®,
1:1 hexane/ethyl acetate) and was used immediately. Decomposition of the trans-γ-
hydroxyenones to the corresponding furan was especially rapid in CDCl3 due to trace
acid.
(E)-4-Hydroxy-1-phenyl-2-buten-1-one (38c).63 The reaction of 1-
triphenylphosphoranylidene-2-phenylethanone (182a) (850 mg, 2.2 mmol) and
glycoaldehyde dimer (120 mg, 1.0 mmol) as per the general procedure afforded (38c)
as a colourless oil (308 mg, 95%); Rf 0.45 (1:1 hexane/ethyl acetate); 1H NMR (300
MHz) δ 1.65 (br s, 1H), 4.49 (dd, J = 3.6, 1.8 Hz, 2H), 7.14 (dt, J = 15.0, 3.6 Hz, 1H),
7.23 (dt, J = 15.0, 1.8 Hz, 1H), 7.46-7.51 (m, 2H), 7.56-7.60 (m, 1H), 7.96-8.00 (m,
2H).
(E)-1-(4-Bromophenyl)-4-hydroxy-2-buten-1-one (38n). The reaction of 1-(4-
bromophenyl)-2-(1,1,1-triphenyl-λ5-phosphanylidene)-1-ethanone (182b) (2.20 g, 4.8
mmol) and glycoaldehyde dimer (240 mg, 2.0 mmol) as per the general procedure
afforded (38n) as an off white solid (830 mg, 86%); mp 77-79 °C; Rf 0.58 (40:60
135
hexane:ethyl acetate); IR (nujol) 3427, 1665, 1614, 1586, 1302, 1012, 794 cm-1; 1H
NMR (200 MHz, d6-acetone) δ 2.96 (br s, 1H), 4.37-4.39(m, 2H), 7.13 (ddd, J = 15.4,
3.2, 1.4 Hz, 1H), 7.25 (ddd, J = 15.4, 1.6, 1.6 Hz, 1H), 7.69-7.75 (m, 2H), 7.88-7.94
(m, 2H); 13C NMR (d6-acetone, 50 MHz) δ 61.4, 122.7, 127.2, 130.3, 131.9, 137.0,
149.4, 188.6; MS (EI) m/z (%): 242 (M+, 81Br, 20), 240 (M+, 79Br, 20), 213 (81Br, 40),
211 (79Br, 40), 185 (81Br, 100), 183 (79Br, 100).
(E)-2,2-Dimethyl-6-hydroxy-4-penten-2-one (38o).63 The reaction of 3,3-dimethyl-
1-(1,1,1-triphenyl-λ5-phosphanylidene)-2-butanone (4.32 g, 12 mmol) with
glycoaldehyde dimer (360 mg, 3.0 mmol) as per the general procedure afforded (38o)
as a colourless oil not separable from triphenylphosphine oxide. Due to the instability
of (38o), further chromatographic separation was not attempted and (38o) was used
crude in the synthesis of tetrahydrofurans.
(E)-5-Hydroxy-3-penten-2-one (38i). 63 The reaction of 1-
triphenylphosphoranylidene-2-propanone (182d) (636 mg, 2.0 mmol) with
glycoaldehyde dimer (100 mg, 0.83 mmol) as per the standard procedure afforded
(38i) as a mixture with triphenylphosphine oxide not readily separable by
chromatography. Due to the instability of (38i), no further chromatographic
purification was attempted as the presence of triphenylphosphine oxide did not
interfere with further reactions of (38i); Rf 0.40 (ethyl acetate); 1H NMR (300 MHz) δ
2.40 (s, 3H), 3.20-3.80 (br s, 1H), 4.30 (dd, J = 2.2, 4.0 Hz, 2H), 6.33 (dt, J = 16.2,
2.2 Hz, 1H), 6.84 (dt, 16.2, 4.0 Hz, 1H).
Preparation of Triphenylphosphine oxide Free (38i). To a stirred solution of
diethyl (2-oxopropyl)phosphonate (350 mg, 2.1 mmol) dissolved in THF (10 ml) was
added glycoaldehyde dimer (120 mg, 1.0 mmol, 1.0 mol. equiv.) followed by lithium
hydroxide (50 mg, 2.1 mmol). The resulting suspension was stirred vigorously for 16
hours. Diethyl ether (20 ml) was added and the mixture filtered. The product was
purified by flash chromatography (florisil®, ethyl acetate) to give a colourless oil
(128 mg, 64%); The spectral properties were identical to those reported above.
(E) 2-Methyl-1-phenyl-4-hydroxy-2-buten-1-one (38p). The reaction of 1-(phenyl)-
2-(1,1,1-triphenyl-λ5-phosphanylidene)-1-propanone (182e) (2.08 g, 4.8 mmol) with
136
glycoaldehyde dimer (290 mg, 2.4 mmol) in THF (15 ml) as per the standard
procedure afforded (38p) as a colourless oil (519 mg, 61%); Rf 0.17 (1:1 hexane/ethyl
acetate); IR (neat) 3429, 3058, 2925, 1644, 1597, 1446, 1332, 1267, 1014 cm-1; 1H
NMR (d6-acetone, 200 MHz) δ 1.88 (dt, J = 1.2, 1.2 Hz, 3H), 4.14 (t, J = 5.5 Hz, D2O
exch., 1H), 4.39 (ddq, J = 5.5, 5.5, 1.2 Hz, 2H), 6.33 (tq, J = 5.5, 1.2 Hz, 1H), 7.42-
7.69 (m, 5H); 13C NMR (50 MHz, d6-acetone) δ 12.5, 59.8, 128.9, 129.9, 132.2,
135.9, 139.3, 146.3, 198.3.
(E) 3-Methyl-4-hydroxy-3-penten-2-one (38q). The reaction of 3-(1,1,1-triphenyl-
λ5-phosphanylidene)-2-butanone (182f) (1.09 g, 3.28 mmol) with glycoaldehyde
dimer (180 mg, 1.5 mmol) afforded (38q) as a colourless oil (317 mg, 93%); Rf 0.42
(40:60 hexane:ethyl acetate); IR (neat) 3420, 2929, 1670, 1652, 1436, 1362, 1026 cm-
1; 1H NMR (d6-acetone, 200 MHz) δ 1.66 (dt, J = 1.0, 1.0 Hz, 3H), 2.62 (s, 3H), 4.14
(br s, 1H), 4.30-4.40 (br m, 2H), 6.71 (tq, J = 5.6, 1.4 Hz, 1H); 13C NMR (50 MHz,
d6-acetone) δ 11.6, 25.3, 59.9, 136.6, 144.0, 199.0.
The Synthesis of THFs from trans-γγγγ-Hydroxyenones (38c,i,n-q).
(±) 2-[(3S,4S,5S)-4-(4-Bromobenzoyl)-5-(hydroxymethyl)tetrahydro-3-furanyl]-1-
(4-bromophenyl)-1-ethanone (171n). To a stirred solution of enone (38n) (750 mg,
3.12 mmol) dissolved in THF (15 ml) was added lithium hydroxide (72 mg). The
resulting suspension was vigorously stirred for 72 hours and then concentrated in
vacuo. Purification by flash chromatography afforded the major product (171n) as a
white solid (443 mg, 59%); mp 63-65 °C; Rf 0.57 (40:60 hexane/ethyl acetate); IR
(nujol) 3445, 2955, 2871, 1681, 1674, 1584, 1397, 1070, 1007 cm–1; 1H NMR (600
MHz) δ 2.00 (br s, 1H), 3.13 (dd, J = 17.0, 7.6 Hz, 1H), 3.18 (dd, J = 17.0, 6.8 Hz,
1H), 3.31 (m, 1H), 3.52 (dd, J = 3.1, 12.5 Hz, 1H), 3.77 (dd, J = 9.0, 5.4 Hz, 1H), 3.87
(dd, J = 12.5, 2.7 Hz, 1H), 3.89 (dd, J = 8.0, 6.8 Hz, 1H), 4.08 (ddd, J = 7.8, 3.2, 3.2
Hz, 1H), 4.29 (dd, J = 8.8, 7.3 Hz, 1H), 7.56-7.63 (m, 4H), 7.71-7.73 (m, 2H), 7.84-
7.87 (m, 2H); 13C NMR (75 MHz) δ 40.7, 41.9, 52.1, 62.1, 73.6, 83.7, 128.6, 128.9,
129.4, 130.0, 132.0, 132.1, 135.1, 135.8, 197.2, 198.9; MS (EI) m/z (%): 465 (MH+-
H2O-H2, 2x 81Br, 5), 463 (MH+-H2O-H2,79Br, 81Br, 10), 461 (MH+-H2O-H2, 2x 79Br,
5), 225 (81Br, 20), 223 (79Br, 20), 185 (81Br, 100), 183 (79Br, 100).
137
(±) 2-[(3S,4R,5R)-4-(4-Bromobenzoyl)-5-(hydroxymethyl)tetrahydro-3-furanyl]-
1-(4-bromophenyl)-1-ethanone (173n). Colourless solid; mp 130-132 °C; Rf 0.55
(40:60 hexane/ethyl acetate); IR (neat) 3442, 2931, 1681, 1584, 1567, 1484, 1398,
1071, 732 cm-1; 1H NMR (600 MHz) δ 1.80-2.00 (br s, 1H), 2.95 (dd, J = 18.0, 6.6
Hz, 1H), 3.03 (dd, J = 18.0, 8.4 Hz, 1H), 3.30-3.36 (m, 1H), 3.59 (dd, J = 12.0, 3.6
Hz, 1H), 3.76 (dd, J = 8.4, 6.0 Hz, 1H), 3.85 (dd, J = 12.0, 3.6 Hz, 1H), 4.27 (dd, J =
8.4, 8.4 Hz, 1H), 4.30 (dd, J = 8.4, 6.0 Hz, 1H), 4.46 (ddd, J = 8.4, 3.6, 3.6 Hz, 1H),
7.52-7.63 (m, 6H), 7.81-7.83 (m, 2H); 13C NMR (150 MHz) δ 37.5, 39.1, 49.0, 63.2,
74.2, 81.5, 128.5, 129.1, 129.3, 129.8, 131.8, 132.1, 135.1, 135.7; MS (EI) m/z
(%):464 (M+-H2O-H2, 2x 81Br, 5), 462 (M+-H2O-H2,79Br, 81Br, 10), 460 (M+-H2O-H2,
2x 79Br, 5), 453 (2x81Br, 5), 451 (79Br, 81Br, 10), 449 (2x79Br, 8), 225 (81Br, 25), 223
(79Br, 25), 185 (81Br, 100), 183 (79Br, 100); HRMS calcd for (M+-H2O-H2)
C20H14O3Br2: calcd, 459.9310; found: 459.9278.
(±) 2-[(3S,3aS,4S,6aR)-4-Hydroxy-4-(4-bromophenyl)perhydrofuro[3,4-b]furan-
3-yl]-1-(4-bromophenyl)-1-ethanone (174n). A white solid which decomposed in
CDCl3 solution, however was stable when crystalline; mp 149.5-155 °C; Rf 0.69
(40:60 hexane/ethyl acetate); IR (nujol) 3353, 1683, 1584, 1068, 1008, 975 cm–1; 1H
NMR (300 MHz, d6-acetone) δ 1.90-2.00 (m, 1H), 2.75-2.90 (m, 3H), 3.28 (dd, J =
8.4, 6.3 Hz, 1H), 3.83 (dd, J = 8.7, 6.3 Hz, 1H), 3.95 (d, J = 9.9 Hz, 1H), 4.18 (dd, J =
9.9, 4.5 Hz, 1H), 4.81 (dd, J = 6.9, 4.5 Hz, 1H), 7.49-7.65 (m, 8H), resonance due to
OH not visible; MS (EI) m/z (%): 465 (MH+-H2O-H2, 2x 81Br, 15), 463 (MH+-H2O-
H2,79Br, 81Br, 20), 461 (MH+-H2O-H2, 2x 79Br, 10), 225 (81Br, 20), 223 (79Br, 20), 185
(81Br, 100), 183 (79Br, 100); Anal. Calcd for C20H18O4Br2: C, 49.82; H, 3.76; Found:
C, 49.76; H, 3.62.
(±) 1-[(3S,4S,5S)-4-(2,2-Dimethylpropanoyl)-5-(hydroxymethyl)tetrahydro-3-
furanyl]-3,3-dimethyl-2-butanone (171o). Colourless oil; Rf 0.25 (60:40
hexane/ethyl acetate); IR (neat) 3454, 2968, 1702, 1479, 1367, 1067 cm-1; 1H NMR
(600 MHz) δ 1.12 (s, 9H), 1.15 (s, 9H), 2.19 (br s, 1H), 2.65-2.69 (m, 2H), 2.72-2.77
(m, 1H), 3.24 (dd, J = 7.2, 4.8 Hz, 1H), 3.54-3.57 (m, 2H), 3.82, (br d, 12.0 Hz, 1H),
3.99 (ddd, J = 6.6, 3.6, 3.0 Hz, 1H), 4.11 (dd, J = 6.8, 6.0 Hz, 1H); 13C NMR (150
MHz) δ 25.8, 26.2, 40.2, 42.0, 43.9, 44.7, 51.1, 62.5, 73.8, 84.3, 214.2, 216.4; MS
138
(EI) m/z (%): 285 (MH+, 10), 267 (100), 253 (10), 209 (20); Anal. Calcd for
C16H28O4: C, 67.57; H, 9.92; Found: C, 67.83; H, 9.63.
(±) 1-[(3S,3aS,4S,6aR)-4-(tert-Butyl)-4-hydroxyperhydrofuro[3,4-b]furan-3-yl]-
3,3-dimethyl-2-butanone (173o). Colourless solid; mp 92-94 °C; Rf 0.55 (ethyl
acetate); IR (nujol) 3346, 1698, 1137, 1083, 997 cm-1; 1H NMR (600 MHz) δ 1.12 (s,
9H), 1.23 (s, 9H), 2.43 (s, 1H), 2.53 (dd, J = 7.5, 1.2 Hz, 1H), 2.63-2.70 (m, 2H),
3.23-3.26 (m, 1H), 3.76 (d, J = 8.4, 3.0 Hz, 1H), 4.04 (dd, J = 9.6, 6.0 Hz, 1H), 4.13
(dd, J = 9.6, 4.2 Hz, 1H), 4.62 (dd, J = 9.0, 6.0 Hz, 1H), 4.65 (ddd, J = 6.6, 6.6, 4.2
Hz, 1H); 13C NMR (75 MHz) δ 25.0, 26.1, 37.5, 38.5, 40.7, 43.8, 53.6, 70.9, 75.7,
83.5, 109.7, 213.0; MS (EI) m/z (%): 285 (MH+, 5), 267 (80), 227 (15),125 (40), 83
(100); Anal. Calcd for C16H28O4: C, 67.57; H, 9.92; Found: C, 67.48; H, 9.79.
(±±±±) 1-[(2R,5S)-5-(3,3-Dimethyl-2-oxobutyl)-1,4-dioxan-2-yl]-3,3-dimethyl-2-
butanone (183). Colourless solid; mp 125 oC (sublimes); Rf 0.77 (60:40 hexane: ethyl
acetate); IR (nujol) 1708, 1127, 1083, 1054 cm-1; 1H NMR (300 MHz) δ 1.12 (s,
18H), 2.32 (dd, J = 17.4, 5.7 Hz, 2H), 2.78 (dd, J = 17.4, 5.4 Hz, 2H), 3.33 (dd, J =
11.4, 10.5 Hz, 2H), 3.79 (dd, J = 11.4, 2.4 Hz, 2H), 3.99 (dddd, J = 10.5, 5.7, 5.4, 2.4
Hz, 2H); 13C NMR (75 MHz) δ 26.0, 38.4, 44.2, 70.8, 71.0, 212.6; MS (EI) m/z (%):
285 (MH+, trace), 143 (20), 125 (100), 57 (80), 41 (40). Anal. Calcd for C16H28O4: C,
67.57; H, 9.92; Found: C, 67.60; H, 9.66.
(+/-) (3S,3aR,7aR)-3-(Hydroxymethyl)-6-methyl-1,3,3a,4,7,7a-hexahydro-4-
isobenzofuranone (184). Colourless oil; Rf 0.48 (ethyl acetate); IR (neat) 3435, 2935,
1651, 1435, 1381, 1054 cm-1; 1H NMR (600 MHz) δ 1.99 (s, 3H), 2.33 (dd, J = 18.6,
6.6 Hz, 1H), 2.43 (br s, 1H), 2.49 (dd, J = 18.6, 6.6, 1H), 2.76 (dd, J = 7.2, 7.2 Hz,
1H), 2.89 (ddddd, J = 7.2, 6.6, 6.6, 6.6, 6.0 Hz, 1H), 3.63-3.68 (m, 2H), 3.81 (br d, J =
11.4 Hz, 1H), 4.00 (dd, J = 8.1, 6.0 Hz, 1H), 4.15 (ddd, J = 6.6, 4.8, 4.8 Hz, 1H), 5.96
(d, J = 0.6 Hz, 1H); 13C NMR (150 MHz) δ 24.5, 30.5, 38.2, 49.1, 64.7, 72.9, 81.2,
125.5, 160.7, 197.6; MS (EI) m/z (%): 183 (MH+, 40), 152 (40),152 (40), 69 (100);
HRMS of 16 (MH+) C10H15O3: calcd, 183.1021; found: 183.1020.
Synthesis of (185) and (186).
139
The reaction of trans-enone (38p) (470 mg, 2.67 mmol) dissolved in THF (5.3 ml)
with lithium hydroxide (61 mg, 2.67 mmol) according to the general procedure
afforded (185) (183 mg, 39 %) and (186) (115 mg, 25%).
(+/-) (2R)-2-[(3S,4S,5S)-4-Benzoyl-5-(hydroxymethyl)-4-methyltetrahydro-3-
furanyl]-1-phenylpropan-1-one (185). Colourless solid; mp 102-104 °C; Rf 0.42
(1:1 hexane: ethyl acetate); IR (neat) 3394, 1673, 1248, 1051, 964, 723 cm-1; 1H NMR
(600 MHz) δ 1.05 (d, J = 7.2 Hz, 3H), 1.39 (s, 3H), 1.80 (br s, 1H), 3.44 (dd, J = 9.6,
9.0 Hz, 1H), 3.53 (dq, J = 10.2, 7.2 Hz, 1H), 3.64 (dd, J = 12.0, 5.4 Hz, 1H), 3.76 (dd,
J = 12.0, 7.2 Hz, 1H), 3.83 (ddd, J = 9.6, 9.6, 9.6 Hz, 1H), 4.26 (dd, J = 8.4, 8.4 Hz,
1H), 4.61 (dd, J = 6.6, 4.8 Hz, 1H), 7.43-7.51 (m, 5H), 7.56-7.58 (m, 1H), 7.78-7.80
(m, 2H), 7.89-7.90 (m, 2H); 13C NMR (150 MHz) δ 12.1, 17.6, 40.7, 50.9, 58.2, 61.8,
71.0, 86.1, 128.2, 128.3, 128.4, 128.8, 131.4, 133.4, 135.7, 138.1, 202.0, 205.8; MS
(EI) m/z (%): 353 (MH+, trace), 321 (10), 238 (20), 201 (40), 105 (100); Anal. Calcd
for C22H24O4: C, 74.97; H, 6.86; Found: C, 74.68; H, 7.14.
X-ray crystallography for (185): Intensity data for a colourless block of (185) were
measured at 183 K on a Bruker AXS SMART CCD using Mo Kα radiation so that
θmax = 30.0°. The H atoms were placed in their geometrically calculated positions and
included in the riding model approximation.
Crystal data for (185): C22H24O4, triclinic, P1(No. 2), a = 6.1275(6); b = 11.248(1), c
= 13.454(1) Å, α = 88.393(2), β = 81.420(2) °, γ = 79.313(2) °, V = 900.9 Å3, Z = 2,
Rgt(F) = 0.056, wRref(F2) = 0.153, T = 183 K.
(+/-) (2S)-2-[(3S,4S,5S)-4-Benzoyl-5-(hydroxymethyl)-4-methyltetrahydro-3-
furanyl]-1-phenylpropan-1-one (186). Colourless oil; Rf 0.20 (ethyl acetate); IR
(neat) 3455, 2976, 2878, 1681, 1596, 1251, 974, 733 cm-1; 1H NMR (600 MHz) δ
1.05 (s, 3H), 1.15 (d, J = 7.2 Hz, 3H), 2.28 (br s, 1H), 3.53 (dd, J = 12.0, 4.2 Hz, 1H),
3.56 (dq, J = 10.2, 7.6 Hz, 1H), 3.67 (dd, J = 12.0, 7.8 Hz, 1H), 3.76 (ddd, J = 10.2,
9.6, 8.4 Hz, 1H), 3.85 (dd, J = 9.6, 8.4 Hz, 1H), 4.34 (dd, J = 8.4, 8.4 Hz, 1H), 4.60
(dd, J = 7.2, 4.2 Hz, 1H), 7.38-7.46 (m, 5H), 7.55-7.57 (m, 1H), 7.84-7.85 (m, 2H),
7.89-7.91 (m, 2H); 13C NMR (150 MHz) δ 13.5, 18.1, 40.5, 50.1, 57.8, 61.7, 70.6,
86.4, 128.0, 128.2, 128.3, 128.7, 130.7, 133.3, 135.2, 138.1, 201.8, 204.3; MS (EI)
m/z (%): 353 (MH+, 15), 345 (15), 321 (50), 238 (55), 201 (55), 105 (100); (186) (40
mg, 0.11 mmol) was dissolved in CH2Cl2 (1 ml) then benzoyl chloride (31 mg, 0.22
140
mmol) and triethylamine (2 drops) was added and the reaction stirred for 3 hours. The
solvent was removed under reduced pressure and the residue purified by flash
chromatography (dichloromethane) to give (187) as colourless crystals suitable for X-
ray structure analysis (28 mg, 56%); mp 132-135 °C; Rf 0.11 (CH2Cl2); IR (nujol)
1723, 1673, 1664, 1595, 1280, 1114, 971, 716 cm-1; 1H NMR (300 MHz) δ 1.17 (s,
3H), 1.19 (d, J = 6.9 Hz, 3H), 3.64 (dq, J = 9.6, 6.9 Hz, 1H), 3.85-4.01 (m, 2H), 4.27
(dd, J = 11.4, 5.1 Hz, 1H), 4.44-4.52 (m, 2H), 4.98 (dd, J = 7.5, 5.1 Hz, 1H), 7.35-
7.60 (m, 9H), 7.85-7.95 (m, 6H); 13C NMR (75 MHz) δ 13.5, 18.2, 40.6, 50.2, 58.3,
63.5, 71.1, 83.7, 128.1, 128.2, 128.3, 128.3, 128.8, 129.6, 129.7, 130.9, 133.0, 133.3,
135.3, 137.8, 166.2, 201.7, 203.3; MS (EI) m/z (%): 439 (MH+-H2O, 10), 397 (20),
351 (20), 105 (100); Anal. Calcd for C29H28O5: C, 76.12; H, 6.38; Found: C, 76.14; H,
6.33.
X-ray crystallography for (187): Intensity data for a colourless plate of (187) were
measured at 183 K on a Bruker AXS SMART CCD using Mo Kα radiation so that
θmax = 30.0°. The H atoms were placed in their geometrically calculated positions and
included in the riding model approximation.
Crystal data for (187): C22H24O4, monoclinic, P1211/c1 (No. 14), a = 9.8981(8) Å; b =
21.431(2) Å, c = 11.576(1) Å, β = 106.849 (2)°, V = 2350.2 Å3, Z = 4, Rgt(F) = 0.067,
wRref(F2) = 0.168, T = 183 K.
(+/-) 2-[(3S,4S,5S)-4-Acetyl-5-(hydroxymethyl)-4-methyltetrahydro-3-
furanyl]butan-2-one (188). Colourless oil; Rf 0.50 (ethyl acetate); IR (neat) 3436,
2979, 2881, 1697, 1657, 1358, 1047 cm-1; 1H NMR (600 MHz) δ 0.98 (d, J = 6.6 Hz,
3H), 1.13 (s, 3H), 2.13 (s, 3H), 2.29 (s, 3H), 2.51 (dd, J = 10.4, 6.6 Hz, 1H), 3.17
(ddd, J = 10.4, 9.6, 8.4 Hz, 1H), 3.39 (dd, J = 9.6, 8.4 Hz, 1H), 3.52 (dd, J = 11.4, 6.0
Hz, 1H), 3.71 (dd, J = 11.4, 6.0 Hz, 1H), 4.14 (dd, J = 6.6, 6.0 Hz, 1H), 4.71 (dd, J =
8.4, 8.4 Hz, 1H); 13C NMR (150 MHz) δ 10.1, 15.8, 26.4, 28.2, 47.2, 49.3, 57.9, 61.4,
70.8, 85.7, 210.2, 210.7; MS (EI) m/z (%): 229 (MH+, 20), 211 (10), 197 (10), 157
(20), 97 (100); HRMS of (M+H) C12H21O4: calcd, 229.1439; found: 229.1441.
The Mixed Dimerisation of 1,2-Dioxines (1b) and (1c). To a stirred solution of 3-
phenyl-3,6-dihydro-1,2-dioxine (1c) (162 mg, 1 mmol) and 3,6-diphenyl-3,6-dihydro-
1,2-dioxine (1b) (238 mg, 1 mmol) in THF (5 ml) was added sodium ethoxide (1.0
ml, 1.0 M, 1 mmol). The reaction mixture was left to stir overnight and then the
141
volatiles were removed in vacuo. The residue was purified by flash chromatography
to afford (171b) (76 mg, 16 %) and (171c) (43 mg, 13 %) as well as the following two
tetrahydrofurans.
(±±±±) 2-{(2S,3S,4S,5S)-4-Benzoyl-5-[hydroxymethyl]-2-phenyltetrahydro-3-
furanyl}-1-phenyl-1-ethanone (189). Colourless oil; (34 mg, 8.5 %); Rf 0.33 (1:1
hexane/ethyl acetate); IR (neat): 3458, 1681, 1597, 1448, 1228, 1048 cm-1; 1H NMR
(600 MHz) δ 2.05 (br s, 1H), 3.02 (dd, J = 16.2, 8.4 Hz, 1H), 3.15 (dd, J = 16.2, 4.2
Hz, 1H), 3.36 (dddd, J = 9.6, 9.6, 8.4, 4.2 Hz, 1H), 3.65 (dd, J = 12.0, 4.2 Hz, 1H),
3.85 (dd, J = 12.0, 3.0 Hz, 1H), 4.31 (dd, J = 9.6, 7.8 Hz, 1H), 4.49 (ddd, J = 7.8, 4.2,
3.0 Hz, 1H), 4.93 (d, J = 9.6 Hz, 1H), 7.26-7.56 (m, 11H), 7.61-7.65 (m, 2H), 7.95-
7.97 (m, 2H); 13C NMR (75 MHz) δ 38.6, 49.1, 52.5, 63.1, 83.7, 86.4, 127.0, 127.9,
128.4, 128.4, 128.6, 128.7, 133.1, 133.3, 136.5, 137.4, 139.9, 198.1, 192.2 (1 masked
aromatic); LSIMS m/z (%): 401 (MH+, 10), 383 (30), 263 (20), 221 (100); HRMS calc
for (MH+, LSIMS) C26H25O4: calcd, 410.1752; found: 401.1736.
(+/-) 2-{(3S,4S,5S)-4-Benzoyl-5-[(S)-1-hydroxy-1-phenylmethyl]tetrahydro-3-
furanyl}-1-phenyl-1-ethanone (190). Colourless solid (70 mg, 17.5 %); mp 130-131 oC (CH2Cl2/hexane); Rf 0.50 (1:1 hexane/ethyl acetate); IR (nujol): 3511, 1689, 1678,
1596, 1225, 1051, 701 cm-1; 1H NMR (600 MHz) δ 2.83 (br s, 1H), 3.08-3.23 (m,
3H), 3.78 (dd, J = 9.0, 6.0 Hz, 1H), 3.84 (dd, J = 6.6, 6.6 Hz, 1H), 4.32 (dd, J = 9.0,
7.2 Hz, 1H), 4.67 (dd, J = 6.6, 5.4 Hz, 1H), 4.68 (d, J = 5.4 Hz, 1H), 7.13-7.63 (m,
11H), 7.69-7.71 (m, 2H), 7.82-7.83 (m, 2H); 13C NMR (75 MHz) δ 41.4, 41.6, 53.0,
73.7, 74.8, 86.9, 126.9, 127.9, 128.1, 128.3, 128.4, 128.5, 128.6, 133.1, 133.3, 136.4,
136.9, 139.8, 198.0, 200.1; MS (EI) m/z (%): 401 (MH+, 5), 383 (MH-H2O, 50), 293
(45), 145 (100), 105 (80); Anal. Calcd for C26H24O4: C, 77.97; H, 6.04; Found: C,
77.50; H, 6.29.
8.7 Compounds Described in Chapter 7.
General Procedure for the Epoxidation of 3,6-Dihydro-1,2-dioxines (1). To a
stirred solution of 1,2-dioxine (1 mmol) in CH2Cl2 (5 ml) was added 70% m-
chloroperbenzoic acid (295 mg, 1.2 mmol) and the reaction left to stir at ambient
142
temperature until complete by TLC. The solvent was removed under reduced pressure
and the products purified by flash chromatography.
(+/-) (1aR,2S,5R,5aS)-2,5-Diphenylperhydrooxireno[2,3-d][1,2]dioxine (194b).
Colourless solid; mp 97-99°C; Rf 0.25 (90:10 hexane/ethyl acetate); IR (nujol) 1492,
740, 695 cm-1; 1H NMR (300 MHz) δ 3.73 (s, 2H), 5.43 (s, 2H), 7.38-7.49 (m, 10H); 13C NMR (75 MHz) δ 52.8, 80.1, 127.8, 128.8, 128.9, 136.0; MS (EI) m/z (%): 254
(M+, 10), 222 (95), 193 (70),131 (50), 77 (100); Anal. Calcd for C16H14O3: C, 75.57;
H, 5.54; Found: C, 75.8; H, 5.58.
(+/-) (1aR,2S,5aR)-2-Phenylperhydrooxireno[2,3-d][1,2]dioxine (194c). Colourless
oil; Rf 0.37 (1:1 hexane/CH2Cl2); IR (neat) 3033, 2913, 1494, 1455, 1036 cm-1; 1H
NMR (300 MHz) δ 3.51 (br d, J = 4.5 Hz, 1H), 3.59 (dd, J = 4.5, 0.6 Hz, 1H), 4.42 (d,
J = 13.5 Hz, 1H), 4.58 (dd, J = 13.5, 1.2 Hz, 1H), 5.38 (s, 1H), 7.39-7.42 (m, 5H); 13C
NMR (50 MHz) δ 48.6, 53.4, 69.2, 81.3, 127.9, 128.8, 129.2, 135.5; MS (EI) m/z (%):
178 (M+, 20), 131 (30), 105 (100); HRMS calcd for C10H10O3: 178.0629; found:
178.0628.
(+/-) (1aS,2R,5aR)-1a-Methyl-5-phenylperhydrooxireno[2,3-d][1,2]dioxine (194e).
Colourless solid; mp 61.5-63°C; Rf 0.43 (CH2Cl2); 1H NMR (300 MHz) δ 1.48 (s,
3H), 3.39 (s, 1H), 4.21 (d, J = 13.2 Hz, 1H), 4.43 (d, J = 13.2 Hz, 1H), 5.37 (s, 1H),
7.35-7.42 (m, 5H); 13C NMR (75 MHz) δ 18.0, 54.5, 60.6, 72.4, 81.4, 127.9, 128.8,
129.2, 135.5; MS (EI) m/z (%): 192 (M+, 20), 160 (95), 105 (90), 43 (100); Anal.
Calcd for C11H12O3: C, 68.73; H, 6.29; Found: C, 68.75; H, 6.51.
(+/-) (1aS,2R,5S,5aR)-2-Methyl-5-phenylperhydrooxireno[2,3-d][1,2]dioxine
(194f). Colourless solid; mp 72-73°C; Rf 0.20 (1:1 hexane/CH2Cl2); IR (nujol) 1492,
1042, 749, 696 cm-1; 1H NMR (300 MHz) δ 1.48 (d, J = 6.6 Hz, 3H), 3.33 (d, J = 4.2
Hz, 1H), 3.55 (d, J = 4.2 Hz, 1H), 4.54 (q, J = 6.6 Hz, 1H), 5.30 (s, 1H), 7.38-7.44 (m,
5H); 13C NMR (150 MHz) δ 15.9, 52.6, 52.9, 74.2, 80.1, 127.9, 128.7, 128.9, 136.0;
MS (EI) m/z (%): 192 (M+, 60), 160 (90), 131 (100), 105 (90); Anal. Calcd for
C11H12O3: C, 68.73; H, 6.29; Found: C, 68.76; H, 6.50.
143
(+/-) (1aS,2R,5S,5aR)-2,5-Dipropylperhydrooxireno[2,3-d][1,2]dioxine (194k).
Colourless oil; Rf 0.31 (1:1 hexane/CH2Cl2); IR (neat) 2961, 2874, 1465, 1380, 1068,
1005, 802 cm-1; 1H NMR (300 MHz) δ 0.96 (t, J = 6.9 Hz, 6H), 1.44-1.57 (m, 6H),
1.60-1.82 (m, 2H), 3.19 (d, J = 0.6 Hz, 2H), 4.24 (dd, J = 7.8, 4.2 Hz, 2H); 13C NMR
(75 MHz) δ 13.8, 18.4, 32.3, 52.3, 77.8; MS (EI) m/z (%): 186 (M+, 20), 154 (50), 125
(70), 57 (60), 43 (100); HRMS calcd for C10H18O3: 186.1255; found: 186.1250.
(+/-) (1aS,2R,5S,5aR)-2,5-Dicyclohexylperhydrooxireno[2,3-d][1,2]dioxine (194l).
Colourless solid; mp 61.5-63 °C; Rf 0.21 (1:1 hexane/CH2Cl2); IR (nujol) 1450, 1100,
1013, 845 cm–1; 1H NMR (300 MHz) δ 1.13-1.29 (m, 10H), 1.64-1.91 (m, 12H), 3.32
(s, 2H), 3.96 (d, J = 6.9 Hz, 2H); 13C NMR (75 MHz) δ 25.7, 25.8, 26.1, 28.3, 29.0,
39.1, 51.3, 81.7; MS (EI) m/z (%): 266 (M+, 20), 249 (15), 234 (10), 83 (100); Anal.
Calcd for C16H26O3: C, 72.14; H, 9.83; Found: C, 72.37; H, 9.86.
(+/-) (1aS,2R,5S,5aR)-2,5-Diisopropylperhydrooxireno[2,3-d][1,2]dioxine (194m).
Colourless oil; Rf 0.15 (1:1 hexane/CH2Cl2); IR (neat) 2964, 1469, 1389, 1370, 991
cm-1; 1H NMR (300 MHz) δ 1.03 (d, J = 6.9 Hz, 6H), 1.03 (d, J = 6.9 Hz, 6H), 2.02
(oct, J = 6.9 Hz, 2H), 3.30 (d, J = 0.9 Hz, 2H), 3.91 (d, J = 6.9 Hz, 2H); 13C NMR (75
MHz) δ 18.4, 18.6, 29.4, 51.2, 82.4; MS (EI) m/z (%): 186 (M+, 5), 101 (30), 71 (70),
43 (100); HRMS calcd for C10H18O3: 186.1255; found: 186.1247.
(+/-) (1aS,2S,5aR)-2-Phenylperhydrooxireno[2,3-d][1,2]dioxine (195c). Colourless
oil; Rf 0.40 (1:1 hexane/CH2Cl2); IR (neat) 2917, 1494, 1454, 1423, 1030 cm-1; 1H
NMR (300 MHz) δ 3.53 (ddd, J = 4.5, 0.9, 0.6 Hz, 1H), 3.66 (ddd, J = 4.5, 4.5, 1.2
Hz, 1H), 4.38 (dd, J = 13.5, 4.5 Hz, 1H), 4.60 (ddd, J = 13.5, 1.2, 0.6 Hz, 1H), 5.37
(d, J = 0.9 Hz, 1H), 7.39-7.42 (m, 5H); 13C NMR (150 MHz) δ 50.5, 51.0, 70.1, 79.8,
128.6, 128.6, 129.3, 134.8; MS (EI) m/z (%): 178 (M+, 60), 131 (90), 105 (100);
HRMS calcd for C10H10O3: 178.0629; found: 178.0634.
(+/-) (1aR,2R,5aS)-1a-Methyl-5-phenylperhydrooxireno[2,3-d][1,2]dioxine (195e).
Colourless oil; Rf 0.53 (CH2Cl2); IR (neat) 2915, 1495, 1454, 1267, 1004, 734, 698
cm–1; 1H NMR (200 MHz) δ 1.51 (s, 3H), 3.39 (s, 1H), 4.20 (d, J = 13.2 Hz, 1H), 4.50
(dd, J = 13.2, 0.4 Hz, 1H), 5.35 (m, 1H), 7.36-7.41 (m, 3H), 7.50-7.54 (m, 2H); 13C
NMR (75 MHz) δ 20.0, 57.3, 57.6, 73.6, 79.5, 128.3, 128.5, 129.1, 135.0; MS (EI)
144
m/z (%): 192 (M+, 20), 145 (70), 131 (80), 105 (100); HRMS calcd for C11H12O3:
calcd, 192.0786; found: 192.0790.
(+/-) (1aS,2S,5R,5aR)-2-Methyl-5-phenylperhydrooxireno[2,3-d][1,2]dioxine
(195f). Colourless oil; Rf 0.28 (1:1 hexane/CH2Cl2); IR (neat) 2996, 2932, 1496,
1454, 1371, 1024, 700 cm-1; 1H NMR (300 MHz) δ 1.75 (d, J = 6.6 Hz, 3H), 3.79
(dd, J = 4.4, 4.4 Hz, 1H), 3.84 (dd, J = 4.4, 1.6 Hz, 1H), 4.77 (dq, J = 6.6, 3.6 Hz,
1H), 5.55 (d, J = 1.6 Hz, 1H), 7.51-7.67 (m, 3H), 7.77-7.82 (m, 2H); 13C NMR (50
MHz) δ 14.9, 52.1, 53.7, 73.4, 79.1, 128.2, 128.7, 128.9, 135.5; MS (EI) m/z (%): 192
(M+, 100), 160 (50), 131 (70), 105 (65); HRMS calcd for C11H12O3: 192.0786; found:
192.0778.
(+/-) (1aS,2S,5R,5aR)-2,5-Dipropylperhydrooxireno[2,3-d][1,2]dioxine (195k).
Colourless oil; Rf 0.48 (1:1 hexane/CH2Cl2); IR (neat) 2961, 2874, 1465, 1379, 1253,
913, 668 cm-1; 1H NMR (200 MHz) δ 0.96 (t, J = 7.2 Hz, 6H), 1.43-1.78 (m, 8H),
3.37-3.38 (m, 2H), 4.21-4.26 (m, 2H); 13C NMR (75 MHz) δ 13.9, 18.5, 31.3, 52.3,
77.2; MS (EI) m/z (%): 186 (M+, 5), 154 (30), 125 (30), 71 (50), 43 (100); HRMS
calcd for C10H18O3: 186.1255; found: 186.1249.
(+/-) (1aS,2S,5R,5aR)-2,5-Dicyclohexylperhydrooxireno[2,3-d][1,2]dioxine (195l).
Colourless oil; Rf 0.54 (1:1 hexane/CH2Cl2); IR (neat) 2925, 2852, 1449, 1254, 983,
911 cm-1; 1H NMR (300 MHz) δ 0.96-1.36 (m, 10H), 1.67-2.00 (m, 12H), 3.42-3.43
(m, 2H), 3.89 (br d, J = 8.7 Hz, 2H); 13C NMR (75 MHz) δ 25.4, 25.7, 26.3, 28.4,
29.5, 37.4, 51.1, 81.8; MS (EI) m/z (%): 266 (M+, trace), 249 (10), 234 (10), 216 (20),
83 (100); HRMS calcd for C16H26O3: calcd, 266.1881; found: 266.1871.
(+/-) (1aS,2S,5R,5aR)-2,5-Diisopropylperhydrooxireno[2,3-d][1,2]dioxine (195m).
Colourless oil; Rf 0.42 (1:1 hexane/CH2Cl2 ); IR (neat) 2961, 2874, 1465, 1379, 1253,
913 cm-1 ; 1H NMR (300 MHz) δ 1.02 (d, J = 6.6 Hz, 6H), 1.06 (d, J = 6.6 Hz, 6H),
2.11 (dsept, J = 9.0, 6.6 Hz, 2H), 3.43-3.46 (m, 2H), 3.78-3.82 (m, 2H); 13C NMR (75
MHz) δ 18.3, 19.3, 28.3, 51.3, 82.8; MS (EI) m/z (%): 186 (M+, trace), 139 (30), 71
(60), 43 (100); HRMS calcd for C10H18O3: 186.1255; found: 186.1256.
Ring-opening Reactions of Epoxy-dioxines.
145
General Procedure for the Ring-opening of Perhydrooxireno[2,3-d][1,2]dioxines
(194) and (195) using Co(II)(SALEN)2. To a stirred solution of Co(II)(SALEN)2 (10
mg, 0.03 mol) in CH2Cl2 (5 ml) at ambient temperature was added 1,2-dioxine (1
mmol) and the reaction left to stir until complete by TLC (3-16 hours). All volatiles
were then removed in vacuo and the product purified by flash chromatography.
{(2R,3R)-3-[(1R)-1-Hydroxy-1-phenylmethyl]oxiran-2-yl}(phenyl)methanone
(196b). Colourless solid; mp 148-150°C; Rf 0.50 (60:40 hexane/ethyl acetate); IR
(nujol) 3408, 1673, 1595, 1252, 1103, 977 cm-1; 1H NMR (600 MHz) δ 2.34 (br d, J =
3.0 Hz, 1H), 3.59 (dd, J = 6.6, 4.5 Hz, 1H), 4.26 (d, J = 4.5 Hz, 1H), 4.57 (dd, J = 6.6,
3.0 Hz, 1H), 7.30-7.68 (m, 8H), 8.01-8.09 (m, 2H); 13C NMR (150 MHz) δ 57.6, 61.5,
71.2, 126.0-140.0 (8 13C signals), 193.9; MS (EI) m/z (%): 335 (MH+-H2O, 8), 316
(15), 290 (20),105 (100); Anal. Calcd for C16H14O3: C, 75.57; H, 5.54; Found: C,
75.31; H, 5.41.
(1aR,2S,4R,4aS)-2,4-Diphenyltetrahydrooxireno[2,3-c]furan-2-ol (198b) / (199b).
Major Anomer: 1H NMR (600 MHz) δ 3.05 (br s, 1H), 3.98 (s, 2H), 5.42 (s, 1H),
7.29-7.69 (m, 10H); 13C NMR (150 MHz) δ 59.9, 62.0, 81.8, 103.0, 126.0-140.0 (8 13C signals).
Minor Anomer: 1H NMR (600 MHz) δ 3.83 (br s, 1H), 4.06 (d, J = 2.4 Hz, 1H), 4.17
(d, J = 2.4 Hz, 1H), 5.48 (s, 1H), 7.29-7.69 (m, 10H).
(+/-) [(2R,3R)-3-(Hydroxymethyl)oxiran-2-yl](phenyl)methanone (196c).163,164 A
colourless oil which decomposed over a period of several days; Rf 0.43 (60:40
hexane:ethyl acetate); IR (neat) 3430, 1688, 1597, 1450, 1229, 1042, 701 cm–1; 1H
NMR (600 MHz) δ 3.61 (dt, J = 5.4, 4.2 Hz, 1H), 3.67 (br dd, J = 12.6, 5.4 Hz, 1H),
3.71 (br dd, J = 12.6, 5.4 Hz, 1H), 4.23 (d, J = 4.2 Hz, 1H), 7.34-7.62 (m, 3H), 8.00-
8.02 (m, 2H); 13C NMR (150 MHz) δ 56.8, 58.0, 59.9, 125.7-128.9 (4 Aryl 13C),
193.5; MS (EI) m/z (%): 178 (M+, 10), 161 (30), 147 (20), 105 (100).
(+/-) (1aR,2S,4aS)-2-Phenyltetrahydrooxireno[2,3-c]furan-2-ol (198c) / (199c).
Major Anomer: 1H NMR (600 MHz) δ 3.76 (d, J = 3.0 Hz, 1H), 3.84 (dd, J = 3.0, 0.6
Hz, 1H), 4.02 (dd, J = 10.8, 0.6 Hz, 1H), 4.20 (d, J = 10.8 Hz, 1H), 7.34-7.62 (m, 5H); 13C NMR (150 MHz) δ 54.8, 60.0, 66.7, 102.0, 125.7-128.9 (4 Aryl 13C).
146
(+/-) [(2S,3S)-3-(Hydroxymethyl)-3-methyloxiran-2-yl](phenyl)methanone (196e). 1H NMR (300 MHz) δ 1.63 (s, 3H), 1.70-1.80 (br s, 1H), 3.63 (br s, 2H), 4.02 (s, 1H),
7.35-7.63 (m, 3H), 7.98-8.01 (m, 2H); 13C NMR (150 MHz, partial) δ 19.3, 63.4,
63.8, 193.1
(+/-) (1aS,2R,4aS)-4a-Methyl-2-phenyltetrahydrooxireno[2,3-c]furan-2-ol (198e) /
(199e).
Major Anomer: Colourless solid; mp 78-81 °C; Rf 0.45 (60:40 hexane:ethyl acetate);
IR (nujol) 3352, 1262, 1105, 1022, 1002, 763 cm–1; 1H NMR (300 MHz) δ 1.61 (s,
3H), 2.82 (br s, 1H), 3.58 (s, 1H), 3.99 (d, J = 9.9 Hz, 1H), 4.08 (d, J = 9.9 Hz, 1H),
7.35-7.63 (m, 5H); 13C NMR (150 MHz, partial) δ 13.6, 69.4, 65.5, 102.8; MS (EI)
m/z (%): 174 (M+-H2O, 5), 161 (60), 123 (20), 105 (100); Anal. Calcd for C11H12O3:
C, 68.73; H, 6.29; Found: C, 69.00; H, 6.41.
Minor Anomer: 1H NMR (300 MHz) δ 1.53 (s, 3H), 3.51 (br s, 1H), 3.65 (s, 1H), 3.87
(d, J = 10.5 Hz, 1H), 4.25 (d, J = 10.5 Hz, 1H), 7.35-7.63 (m, 5H).
(+/-) {(2R,3R)-3-[(1R)-1-Hydroxyethyl]oxiran-2-yl}(phenyl)methanone (196f).
Colourless solid; mp 90-92 °C; Rf 0.50 (60:40 hexane/ethyl acetate); IR (nujol) 3448,
2924, 2854, 1677, 1597, 1450, 1274, 1234, 1065, 982, 964, 705 cm-1; 1H NMR (600
MHz) δ 1.31 (d, J = 6.6 Hz, 3H), 3.29 (dd, J = 6.6, 4.8 Hz, 1H), 3.57 (dq, J = 6.6, 6.6
Hz, 1H), 4.16 (d, J = 4.8 Hz, 1H), 7.49-7.53 (m, 2H), 7.59-7.61 (m, 1H), 8.04-8.06
(m, 2H); 13C NMR (150 MHz) δ 20.5, 57.4, 61.6, 64.7, 128.5, 128.6, 133.8, 135.5,
193.9; MS (EI) m/z (%): 192 (M+, 4), 149 (10), 123 (20), 105 (90), 86 (100); Anal.
Calcd for C11H12O3: C, 68.73; H, 6.29; Found: C, 68.85; H, 6.40.
X-ray crystallography for 4b. Intensity data for a Colourless crystal were measured
at 183(2) K on a Bruker AXS SMART CCD using Mo Kα radiation so that θmax =
30.1°. The structure was solved by direct-methods and refined (anistropic
displacement parameters, H atoms in their calculated positions and a weighting
scheme w = 1/[σ2(Fo2) + 0.0834P2 + 0.1066P] where P = (Fo
2 + 2Fc2)/3 on F2 with
SHELXL-97.
Crystal data: C11H12O3, M = 192.21, monoclinic, P21/c, a = 10.9197(12), b =
11.1051(12), c = 8.7057(9) Å, β = 112.301(2) °, V = 976.73(18) Å3, Z = 4, Dx = 1.307,
F(000) = 408, μ = 0.095 mm-1, no. of unique data = 2850, no. of parameters = 128, R
(all data) = 0.055, wR (all data) = 0.149, ρ = 0.41 e Å-3.
147
(+/-) (1aR,2R,4R,4aS)-2-Methyl-4-phenyltetrahydrooxireno[2,3-c]furan-2-ol
(198f) / (199f).
Major Anomer: 1H NMR (600 MHz) δ 1.38 (d, J = 7.2 Hz, 3H), 3.64 (d, J = 3.0 Hz,
1H), 3.72 (d, J = 3.0 Hz, 1H), 4.45 (q, J = 7.2 Hz, 1H), 7.27-7.34 (m, 3H), 7.53-7.55
(m, 2H); 13C NMR (150 MHz) δ 19.0, 59.1, 61.1, 75.0, 101.9, 126.4, 127.8, 128.1,
140.8.
Minor Anomer: 1H NMR (600 MHz) δ 1.25 (d, J = 6.6 Hz, 3H), 3.63 (d, J = 3.0 Hz,
1H), 3.93 (d, J = 3.0 Hz, 1H), 4.58 (q, J = 6.6 Hz, 1H), 7.27-7.34 (m, 3H), 7.53-7.55
(m, 2H).
(+/-) (1aR,2S,4R,4aS)-2,4-Dipropyltetrahydrooxireno[2,3-c]furan-2-ol (198k) /
(199k).
Major Anomer: Colourless oil; Rf 0.50 (70:30 hexane/ethyl acetate); IR (neat) 3422,
2961, 1456, 1423, 1380, 1237, 1146, 1009; 1H NMR (300 MHz) δ 0.93-0.99 (m, 6H),
1.35-1.85 (m, 8H), 2.28 (s, 1H), 3.61 (d, J = 3.0 Hz, 1H), 3.62 (d, J = 3.0 Hz, 1H),
4.09 (dd, J = 8.4, 5.7 Hz, 1H); 13C NMR (75 MHz) δ 13.9, 14.2, 17.3, 19.0, 35.4,
38.8, 57.8, 58.4, 78.5, 103.3; MS (LSIMS) m/z (%): 187 (MH+, 25), 169 (100);
HRMS calcd for (M+H) C10H19O3: 187.1334; found, 187.1332.
Minor Anomer: 1H NMR (300 MHz) δ 0.93-0.99 (m, 6H), 1.35-1.85 (m, 8H), 3.22 (s,
1H), 3.62 (d, J = 3.0 Hz, 1H), 3.66 (d, J = 3.0 Hz, 1H), 4.20-4.24 (m, 1H); 13C NMR
(75 MHz) δ 13.8, 14.4, 16.4, 18.6, 35.1, 39.7, 60.7, 61.4, 77.9, 103.3.
(+/-) (1aR,2S,4R,4aS)-2,4-Dicyclohexyltetrahydrooxireno[2,3-c]furan-2-ol (198l) /
(199l).
Major Anomer: Colourless solid; mp 81-83 °C; Rf 0.38 (80:20 hexane/ethyl acetate);
IR (nujol) 3400, 1304, 1241, 1021, 866 cm–1; 1H NMR (600 MHz) δ 0.95-1.95 (m,
22H), 2.16 (s, 1H), 3.62 (d, J = 3.0 Hz, 1H), 3.68 (d, J = 3.0 Hz, 1H), 3.73 (d, J = 9.6
Hz, 1H); 13C NMR (150 MHz) δ 25.5, 25.6, 25.9, 26.0, 26.2, 26.2, 26.3, 28.2, 29.3,
29.6, 40.6, 43.9, 56.2, 58.0, 83.4, 104.6; MS (EI) m/z (%): 266 (M+, 10), 248 (30), 230
(40), 83 (90), 55 (100); Anal. Calcd for C16H26O3: C, 72.14; H, 9.83; Found: C, 71.85;
H, 9.83.
Minor Anomer: 1H NMR (600 MHz) δ 0.95-1.95 (m, 22H), 3.14 (s, 1H), 3.72 (d, J =
3.0 Hz, 1H), 3.75 (d, J = 3.0 Hz, 1H), 3.89 (d, J = 9.0 Hz, 1H); 13C NMR (150 MHz,
partial) δ 26.1, 26.3, 27.2, 28.8, 29.1, 40.3, 44.3, 60.9, 82.9, 104.5
148
(1aR,2S,4R,4aS)-2,4-Diisopropyltetrahydrooxireno[2,3-c]furan-2-ol (198m) /
(199m).
Major Anomer: Colourless solid; mp 66-68 °C; Rf 0.52 (60:40 hexane/ethyl acetate);
IR (nujol) 3363, 1414, 1211, 1060, 1010, 868 cm-1; 1H NMR (600 MHz) δ 1.0 (d, J =
6.6 Hz, 6H), 1.05 (d, J = 6.6 Hz, 6H), 1.81 (d sept, J = 9.0, 6.6 Hz, 1H), 2.04 (sept, J
= 6.6 Hz, 1H), 2.11 (s, 1H), 3.63 (d, J = 3.0 Hz, 1H), 3.67 (d, J = 3.0 Hz, 1H), 3.68 (d,
J = 9.0 Hz, 1H); 13C NMR (150 MHz) δ 18.0, 19.4, 31.9, 33.8, 56.5, 58.2, 84.7,
105.0; MS (EI) m/z (%): 187 (M++H, 10), 169 (100), 97 (40), 71 (70); Anal. Calcd for
C10H18O3: C, 64.48; H, 9.74; Found: C, 64.24; H, 9.96.
Minor Anomer: 1H NMR (600 MHz) δ 0.96 (d, J = 6.6 Hz, 6H), 1.04 (d, J = 6.6 Hz,
6H), 1.63 (d sept, J = 9.3, 6.6 Hz, 1H), 1.93 (sept, J = 6.6 Hz, 1H), 3.12 (s, 1H), 3.72
(d, J = 3.0 Hz, 1H), 3.76 (d, J = 3.0 Hz, 1H), 3.84 (d, J = 9.3 Hz, 1H); 13C NMR (150
MHz) δ 15.6, 18.7, 30.8, 34.3, 61.5, 60.9, 84.0, 105.1.
(+/-) {(2R,3R)-3-[(1S)-1-Hydroxyethyl]oxiran-2-yl}(phenyl)methanone (197f).
Colourless solid; mp 69-71 °C; Rf 0.50 (60:40 hexane:ethyl acetate); IR (nujol) 3400,
1690, 1597, 1226, 1093, 1038, 984, 707 cm-1; 1H NMR (600 MHz) δ 1.13 (d, J = 6.6
Hz, 3H), 2.31 (br d, J = 3.0 Hz, 1H), 3.38 (dd, J = 7.2, 4.8 Hz, 1H), 3.56 (ddq, J = 6.6,
6.6, 3.0 Hz, 1H), 4.28 (d, J = 4.8 Hz, 1H), 7.33-7.65 (m, 3H), 7.99-8.01 (m, 2H); 13C
NMR (150 MHz) δ 19.0,57.5, 67.4, 65.4, 125.7-139.1 (4 Aryl 13C), 193.1; MS (EI)
m/z (%): 193 (MH+, 15), 175 (40), 154 (100), 137 (80); HRMS of C11H13O3 (MH+):
calcd, 193.0864; found: 193.0864.
(1aR,2R,4S,4aS)-2-Methyl-4-phenyltetrahydrooxireno[2,3-c]furan-2-ol (200f) /
(201f).
Major Anomer: 1H NMR (600 MHz) δ 1.42 (d, J = 6.0 Hz, 3H), 3.21 (br s, 1H), 3.67
(dd, J = 3.0, 0.6 Hz, 1H), 3.70 (d, J = 3.0 Hz, 1H), 4.32 (dq, J = 6.0, 0.6 Hz, 1H),
7.33-7.60 (m, 5H); 13C NMR (150 MHz) δ 15.2, 57.7, 60.7, 72.9, 102.2, 125.7-139.1
(4 Aryl 13C);
Minor Anomer: 1H NMR (600 MHz) δ 1.43 (d, J = 6.6 Hz, 3H), 3.71 (dd, J = 3.0, 0.6
Hz, 1H), 3.80 (d, J = 3.0 Hz, 1H), 4.24 (dq, J = 6.6, 0.6 Hz, 1H), 7.33-7.60 (m, 5H); 13C NMR (150 MHz) δ 16.3, 60.1, 61.6, 74.0 104.0, 125.7-139.1 (4 Aryl 13C).
149
(+/-) (1aR,2S,4S,4aS)-2,4-Dicyclohexyltetrahydrooxireno[2,3-c]furan-2-ol (200l) /
(201l).
Major Anomer: Colourless solid; mp 94-95 °C; Rf 0.19 (CH2Cl2); IR (nujol) 3400,
1304, 1241, 1021, 866 cm–1; 1H NMR (600 MHz) δ 0.97-1.32 (m, 10H), 1.58-1.96
(m, 12H), 2.20 (s, 1H), 3.58 (d, J = 3.0 Hz, 1H), 3.63 (dd, J = 3.0, 0.6 Hz, 1H), 3.70
(br d, J = 8.4 Hz, 1H); 13C NMR (150 MHz,) δ 25.7, 25.8, 26.0, 26.0, 26.3, 26.4, 26.4,
27.9, 29.2, 30.1, 38.7, 43.6, 54.3, 57.1, 80.8, 104.2; MS (EI) m/z (%): 266 (M+, 4),
248 (15), 230 (30), 83 (100); HRMS of C16H26O3: calcd, 266.1887; found: 266.1881.
Minor Anomer: 1H NMR (600 MHz) δ 0.97-1.32 (m, 10H), 1.58-1.96 (m, 12H), 2.93
(s, 1H), 3.54 (dd, J = 7.8, 1.2 Hz, 1H), 3.65 (d, J = 3.0 Hz, 1H), 3.73 (dd, J = 3.0, 1.2
Hz, 1H); 13C NMR (150 MHz, partial) δ 25.7, 26.0, 26.2, 26.3, 26.3, 26.8, 39.9, 44.2,
58.5, 59.2, 82.6, 104.7.
150
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